Eagler's Nest

Airframes => Single Seaters => XL => Topic started by: Bob Wood on June 15, 2014, 08:06:22 AM

Title: Dual mikuni's 28's running rich
Post by: Bob Wood on June 15, 2014, 08:06:22 AM: I finished my XL last week and been running it up working out bugs and setting carbs. I swapped out the stock 200 jets for 170's per Scott Casler and other forum recommendations. My motor. Is a 37 hp Mosler. I get 3100 static (54x22 TN prop)and seems to run very well even at very low idle.Timing and valves set right on..my question is black sooty plugs really sooty black on left and a little less on the right. I left the jet clips in the middle position as I received them did not change them when I put in the 170,s. I started with the mixture screws out 1.5 turns now at 1 turn out . I am thinking I need to move the jet clips up to lean this thing out. Do I go to the first or second notch and keep the mixture screws out 1.5 turns , or is there a system to do this. From my motorcycle work I am thinking I need to end up about 1.5 out on the mixture and leaner on the needle clips. After I get good looking plugs I will fine tune with the EGT .
Any direction here will be appreciated

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on June 15, 2014, 09:15:38 AM: Quote from: Bob Wood on June 15, 2014, 08:06:22 AM
I finished my XL last week and been running it up working out bugs and setting carbs. I swapped out the stock 200 jets for 170's per Scott Casler and other forum recommendations. My motor. Is a 37 hp Mosler. I get 3100 static (54x22 TN prop)and seems to run very well even at very low idle.Timing and valves set right on..my question is black sooty plugs really sooty black on left and a little less on the right. I left the jet clips in the middle position as I received them did not change them when I put in the 170,s. I started with the mixture screws out 1.5 turns now at 1 turn out . I am thinking I need to move the jet clips up to lean this thing out. Do I go to the first or second notch and keep the mixture screws out 1.5 turns , or is there a system to do this. From my motorcycle work I am thinking I need to end up about 1.5 out on the mixture and leaner on the needle clips. After I get good looking plugs I will fine tune with the EGT .
Any direction here will be appreciated

Bob

Bob,
I think Joe Spencer is running a 160 & a 150 main jet on his 45 which requires more juice than your 37... Leave the Circlip in the center slot for now... Your rings may not be fully seated yet and that leaves the compression down some and a little oil getting into the combustion... Put in 160 jets & run it some more -

Joe is traveling today and will weigh in later for sure...
Steve
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on June 15, 2014, 09:43:51 AM: yeh that's right a 150 and a 160. I would expect the 37 to need several sizes smaller
do you have dual egt? the power comes on above 1300...1350-1400 is where mine sings. since we don't have much power we need all we can get out of it and EGT was the only way I could reliably get max tune out of it.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on June 15, 2014, 09:46:36 AM: disregard the egt question I see you have those. joe
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on June 15, 2014, 10:03:33 AM: This graphic is central to understanding a properly sized Mikuni VM carb

(https://www.eaglersnest.com/forum/gallery/3-150614115011.jpeg)

A new Edition of the Mikuni VM Tuning Manual is attached:

(http://www.mikuni.com/pdf/vmmanual.pdf)
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on June 15, 2014, 10:47:56 AM: Running mogas seems to result in sooty looking plugs regardless of jetting (unless extremely lean?...but it probably won't run well if it gets very lean...). Also expect to see sooty exhaust stacks. EGT is probably the only accurate way to sort out jetting.

Adjust mixture by ear to get smooth idle and smooth transition from idle. Your engine won't spend much time running on the needles, it will be near full throttle most of the time. If the needles are off, you won't hurt the engine.....it'll get your attention by misfiring...... ;)

Unlike 2-strokes, these engines are bullet-proof even if jetted too lean as long as the timing is in spec.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on June 15, 2014, 12:12:48 PM: Quote from: Steve on June 15, 2014, 10:03:33 AM
This graphic is central to understanding a properly sized Mikuni VM carb

(https://www.eaglersnest.com/forum/gallery/3-150614115011.jpeg)

A new Edition of the Mikuni VM Tuning Manual is attached:

(http://www.mikuni.com/pdf/vmmanual.pdf)

I haven't studied the size chart in detail but do wonder from personal experience with the 45/vm28s if the 28s might be too large for the 37 horse for optimum power and efficiency. We should find out with this 37 and it's EGTs
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on June 15, 2014, 01:08:21 PM: I have felt for some time that the Mikuni VM26-626 (a popular Japanese made alum body Mikuni) is the better choice for the smaller motors 32-37 HP...

Let's see how Bob does with his 37 hp motor...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on June 15, 2014, 07:51:32 PM: So the process is to go down from my current 170 jets to 140. 150 Or 160. Until I can get the 1300
To 1400 on the EGT. I must be so rich and cool now with the 170 jets because my EGT does not even hit the 900 min on my gauge. If I start with a jet too small say 140 will the engine just get doggy at high rpm due to lack of fuel?
Thanks for the help on this!!
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on June 15, 2014, 08:10:45 PM: I'd put a 140 in the richer cyl and a 150 in the other - run it at different /varying power settings 2900 rpm - WOT for 1/2 an hour...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 18, 2014, 07:22:24 AM: Still at this jetting task to get to 1300-1400egt. With my mikuni 28 and my 37 hp I have a 140 jet on one side and a 150 on other. My needle clip Is in the middle I only show 500 on EGT and 1 plug very black, other showing some white porcelain .Running 92 no ethanol mo gas. I have been running for about 20 min at 2000 -3100 rpm and see cht less than 250 and EGT 450-500. Am I not running long enough? My next step is to go one notch leaner on the needle clip to the second notch from top. This is my first time at this is there a better procedure. My engine is broken in has about 40 hours on it. Last flown with single carb until my dual conversion.
Help, scratching my head here!,,

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 18, 2014, 07:47:59 AM: i wouldn't change the needle yet.
where are your probes located? i run mine about 2-3" from the exhaust flange
it sounds like your egt setup may be suspect. are you sure you got the right probes for your gauge? if the thing is running atall it oughta be higher than 500 when the power is up. mine runs about 800 or so at idle.
have you tried a smaller jet for the cyl with the black plug? i'd keep going down on that til i got them running more toward gray...just jet it with the plug color til you get it in the ballpark then fine tune it with the egt
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 18, 2014, 08:27:34 AM: My EGT probe is 3 1/4" from flange....Maybe move it up an inch" to 2"...... I am running the Belite LED combo gauge for EGT and CHT on one side only. I was going to swap the probes over to get set up or put in 2 probes ans swap out at the gauge for set up. Belite recommends the falcon probes which I am running.

Since I am already down to 140 and 150 I figured I should move the needle clip. try 135 jets first maybe??

If I move the needle clip 1 notch leaner and it is too lean will it miss at full throttle?
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 18, 2014, 08:35:17 AM: One other thing I forgot to mention, the Belite gauge has a minimum EGT temp of 900 and a min CGT of 250....As I said i am not hitting minimums on either. After 20 min or so of running I shut down and my CGT is like 230. with laser thermometer
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 18, 2014, 10:59:50 AM: i never moved the clip on mine still in the middle
yeah i would just go smaller jets til got the plugs looking about right then adjust for the egt. i wouldn't be surprised to see the 37 end up with several size smaller jets than 150 i got a 150 on one side of my 45. with the low egts you got; assuming they're correct, i'd try 125s for hopefully an obvious difference in plug color/temps and adjust from there. since youre running one sooty plug i don't think youre on the lean side of peak and i wouldn't think 125s are gonna put you lean of peak either. but watch for that. running premium youre not likely gonna make it detonate even if too lean. the comp is only 8:1 so you got all kinda margin. only reason Casler says premuim fuel is cause it's air cooled and runs at relatively high power routinely(as compared to say in a bug)
trial and error
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 18, 2014, 11:06:35 AM: Thanks for this Joe, I am also going to move up my Probe to 2" and see if that matters.

Will report back with the 125's results
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 19, 2014, 09:55:04 AM: Jetting 37 HP update:

I put in 130's in both sides last night only because I could not get 125's at my local cycle shop. My EGT is on #4, and it is still very black and sooty...On #2 the CGT side it was very clean and looked good. Is it likely #4 is still too rich to get above 900? My LED gauge has a 900 minimum reading...

So i still get no minimum 900 degree EGT reading on #4 and when I shut down I took a temp reading on the head where my CHT probe is under the head bolt. It read right at 230 under the LED gauge minimum 250 mark.

I checked my probe location on #4 for EGT and I am 2" below the bottom end of the pipe flange. Seem ok....

So i am going to try a 120 in the #4 EGT side. I also am going to install another egt probe on the #2 side.

Any thoughts? when you are close to EGT of 1400 ..say 1200, how much of a jet reduction does it take to gain 100 degrees?

I kept my needle clip in the center slot on both carbs

Thanks for the help,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on August 19, 2014, 01:47:17 PM: Bob:
Use a Multimeter with the Milli-volt scale and check the EGT probe voltages per attached table:
Steve
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 19, 2014, 01:49:49 PM: Perfect !! thanks steve.
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 19, 2014, 02:43:59 PM: maybe you told us this in the OP...have you checked the float level for the rich cylinder? also have you verified that the float needle is seating?
as a check on the egt gage try swap it over to the nice running cylinder and see what thats doing. if its in the ball park say 1100-1300 and you got near the same jets both cylinders i would start looking at stuff besides the jets too. you're getting a nice hot spark at the plug on the rich cylinder? i'm starting to think i would try swap carbs over and see what you get then. should be a reversal if its in the carb. no change if it's something else
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 20, 2014, 08:17:35 AM: Thanks Joe, good stuff here. On the floats...should I just see if both are the same, or is there a height measurement I should set? am going to take volt meter measurements on the probes and see the differences between the good and rich side also.

On the gas spitting situation it seems like the carbs are vibrating on the hoses and shaking fuel out of the vents.. Maybe the floats are jumping around and opening the float needle....

Will be back you after my next run up.
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 20, 2014, 10:38:51 AM: IIRC the top of the float should be set level with the top of the bowl. if the rich carb is set too high that could be the problem. mine drip and spit randomly and that could mask a high float overflowing the bowl. basic carb stuff...
the 37 doesn't hit as hard or shake as much as the 45...maybe when you get the carbs balanced it will settle down and stop shaking and spitting so much. if not a brace would be good. here's a pic of mine
IMO dual egts are important for fine tuning these things. if we don't get the carbs closely balanced then its like 2 diff power motors hooked to the same crank...they fight one another. course that costs power and we don't have much. and the routine daily temp swings will affect the egt so its good to know what its doing. if you got it tuned to say 1350 for summer afternoon temps and go out and do a cool early morning flight the egt may go up as much as 100 degrees and nor we/re over the 1400 max.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 20, 2014, 12:36:20 PM: Many thanks Joe, I will report back.
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 22, 2014, 08:27:58 AM: I checked my float levels yesterday, sure enough the rich side was set richer than the lean side by about 2mm. So I evened them out and will run up and take probe voltage measurements to see what is up with EGT. I ahve my second probe on order.... Raining so no runup....

So i went back to the Mikuni handbook and looked at float height measurements for the VM28 and I see it says 15-17mm. That seems even lower than where I am now. So i am going to recheck after my run up. With the independent float set up you just measure the plate height when the tab just touched the needle. I did not do this I just compared my lean to rich and made them the same...

Do you guys go with the Book float setting. After seeing this set up it is easy to see why the carbs spit fuel. My rich side was the only side spitting alot. Just a couple drops on the other side.

Thanks for the help, I feel like I am making headway....
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 25, 2014, 09:06:47 AM: I ran up again with a 120 main on #4 carb(Richer side) and it is still very sooty and black. The #2 side looks nice and clean with the 130 in it.

I took EGT readings with the volt meter and got 19.8 on the lean side #2 and my gauge was indicating about 925-950 on the rich side #4 so very close to each other.

So I was going to try 100 & 110 main jet in the rich side, and maybe110- 115 in the lean side to try to get up to 1300 or so.

The other interesting thing is I checked my air screws at 1000 RPMS. I have had them both set at 1 1/4 turns out and went in and out 1/4 turn to see if I could gain any RPMs.. No big effect (smooth acceleration) I left them at 1 1/4 out. Then I closed each one and opened back up to 1 1/4 while the engine was running at 1000 RPMs. On #2 the leaner side the engine idled way down seemed like it was going to quit...On the rich side there was very little effect when I close the air screw ( slight RPM reduction)

Is this telling me the rich side is so rich already the extra richness ( when closing the air screw) is not effecting anything. And on the lean side the extra richness is bogging things down? Seems logical , am i correct on this?

So I continue decreasing jet size to increase the EGT. Looking for 1300-1350 or so....correct?
Thanks for any suggestions.
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 25, 2014, 04:45:01 PM: >>>On the rich side there was very little effect when I close the air screw ( slight RPM reduction)

not sure which airscrew youre talking about but if there's no change when rotating that indicates its probably stopped up. a stopped up airscrew would probably cause it to be rich. have you removed it and checked for that? i'd blow air thru it put it back in and see if any change. you should have gotten at least some improvement on the rich side with the jet changes and float adjustment. since it sounds like you haven't seen any improvement atall i'd look elsewhere for a while...like the airscrew and possibly casting scale in the passages inside the carb altho that's not very likely i've heard that it's happened. are you running air filters? no obstruction there? try taking the filter off and running it. i think youre short on air somewhere. you haven't said anything about the choke.

have you got this manual?

http://www.mikuni.com/pdf/vmmanual.pdf

Sam and SK yall got any more ideas?
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on August 25, 2014, 05:20:22 PM: Joe: I think you're right on track with observations re: the still rich carb - maybe switch carbs to eliminate cyl or ign anomalies... Steve
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 25, 2014, 06:33:28 PM: Ok ,did another run up tonight and I went from a 120 to a 105 jet and went from 925 or so to a about 1050 or 1100. EGT. That was the rich cylinder. I am using a motorcycle air filter that seems like good flow when I blow through it. I will do a run up with no filter and see what happens. I am waiting for a probe to test the lean side. I was going to swap carbs to see if it is carbs..I was going to try a 95 or so down from the 105 to see where the EGT goes. After I went to the 105 jet the carb did stop spitting fuel from the vents.......

Does it seem like a 95 jet will get me up to 1300 pr so?

Think I am on the right track?
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 26, 2014, 05:27:30 AM: i wouldn't expect it to take more than a couple sizes diff to match up 2 otherwise same same cylinders. believe you said you had a 120 on the lean side. youre down to a 105 jet now which leads me to think the problem is air and that's where i'd be looking at this point. seems all youre doing now is matching the fuel to a restricted air source
that non responsive air screw is job one. if that doesn't fix it and the air filter removal doesnt do it then next is swap the carbs side to side. i wouldn't do anything else til i had done those 3 things one thing at a time. always one thing at a time and then test.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 26, 2014, 05:33:39 AM: i looked back and see you have a 130 in the lean side. that sounds about right for a 37...my 45 is a 150 and a 160 IIRC. naw, that rich side definitely looks like it has something besides the jetting going on.
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on August 26, 2014, 05:59:18 AM: Yep, the rich carb needs to come completely apart, sounds like a restriction somewhere. Force air through all the ports and passages, make sure everything is clear.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 26, 2014, 06:10:10 AM: Bob are you running a fuel pump? If so check that you don't have a gravity flow needle/seat on that rich side. it's bigger and a pump might overpower the float thru that bigger hole.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 26, 2014, 09:46:04 AM: No fuel Pump. I did check that out per this forum a while back. I have the gravity jets and no fuel pump.

I will take that carb apart and blow out all passages.

I will then run up again with and without an air filter. (What is the recommended air filter anyway?)

RE: air screw adjustment:

I should see an RPM increase as I lean out the air screws( screw turned out to lean) correct.? So if both are now at 1 1/4 out I will turn 1/4 in or out to see effect and adjust to max rpm increase. Set at 1000 RPMs to do this adjustment?

If I still get odd results I will swap carbs from side to side....

Thanks vey much for the help!! Will report back

I really want to fly this thing!!
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 27, 2014, 08:48:23 AM: Ok, looking better here. I cleaned out the rich carb and got the air screw working. I adjusted them both at about 1000RPM and acceleration seems smooth at low end. ended up 2 turns out on both. Was at 1 1/4 seems to have smoothed it out.

I put back in a 130 main and it run up to 1000 degrees. Before it was less than 900( min on my gauge) Today I will go down to the 120 and see where it goes.
Waiting for my probe for the other side to see there that is at.

I also removed my air filters and clamped fiberglass window screen over each one until I get foam ones or whatever. I found little bits of black rubber that rubbed off the the airfilters in the intake....Must have sucked it up....

I will advise when I run up the 120 today.

Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 28, 2014, 08:50:04 AM: RE: rich #4 cylinder

Went back out and put a 120 in the rich side #4 (down from the 130) Ran it up and got 1050 drgrees only another 50 up from the 130.....

Pulled the plug and still very sooty rich...

I got my other EGT Probe to install today on the leaner #2 side.

I am going to check points, timing, valves, rotor, and cap today. run up again take readings. swap carbs around and run up again to see is it is carb related or the motor causing richness in #4.

Will report back
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on August 28, 2014, 09:38:48 AM: Keep in mind that burning auto gas will often result in sooty plugs and exhaust stacks. That doesn't explain the difference in plugs on each side but the plugs in my 45 always have soot. A shot of brake cleaner removes the soot and reveals the true color of the insulator.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 28, 2014, 09:59:08 AM: once you get the other egt installed things should get much clearer. i would sure install it before swapping the carbs around . in fact i'd install it before i did *anything* else to it...we don't want to tamper with the evidence before we know what it is.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 29, 2014, 08:06:27 AM: EGT Probe on #2, will run up when the rain quits.

I double checked spark strength and point gap and found the point gap to be way off, we are supposed to be at .020 with the 009 distrib right? I was about 1/2 that....

so re-timed with a light gun after resetting points. Spark Plug gap is supposed to be .030 or .035? I have 2 numbers in my notes..

Will advise ETG on both after run up.

I am hoping the weak spark is my problem with richness...

Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 29, 2014, 10:04:24 AM: ahhh...the spark.i looked back and we talked about that back on page one i think it was. maybe that's
the problem. i don't know anything about the distributor just the mag so cant help with that. when i was looking back for the spark question i saw that your motor is a Mosler so that stuff I said about compression and such may be wrong. i was thinking it was a Casler which is the only one i know anything about. doesn't matter anyway.
you're gonna find it...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 29, 2014, 10:10:12 AM: Ya I turned out the lights in the hanger and did spark tests and it just looked a little weak.....So got to thinking I mat have adjusted timing wiht the light after I set the points..... fingers are crossed!!

Will be back to you later today,
thanks,,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 30, 2014, 12:50:12 PM: Ok I got the second probe on and ran it up with a 120 jet on the #4 and a 115 on the leaner side and they ran
As 1000 -1050 on # 4 and about 950 on # 2. The plugs looked lots leaner white porcein and clean electrode still sooty on base ring. Still not sure how to get all the way up to 1350. One other thing I noticed is my cap is worn where the index tab is and can be moved 1/8" side to side. I did a spark test and it seemed to effect spark intensity. So I went out and got a new cap and rotor to run up again. How many sizes does one normally go down to get from 1000 to 1350 on the EGT

Sort of puzzled
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 30, 2014, 01:49:43 PM: when doing a full throttle static runup does the motor continue to respond to increasing throttle all the way to wide open(slide all the way up) or does it top out at say for instance 3/4 of the slide range? in other words...you know on the throttle lever or handle or whatever you have where full open slide is...open the throttle up and see if max rpm is reached before reaching the full open slide position or simultaneously reaches top rpm and full throttle lever movement.
what we're trying to eliminate with this is if the carbs are too big for the motor or not. i know folks have run 28s on similar size and smaller motors and even 32s or so. but i don't know if those same folks are running egts and trying for max tune. they may be somewhere way short of max power...as far as i know we,ve never seen info to that effect on the Eaglers forums. on the mikuni app chart i think the 28s may be above the recommended size for your motor but check me on that. on that same chart IIRC 28s are indicated for the 45 and even 26s.
you got them within about 100F of one another and thats fine at this point...now you either gotta reduce fuel or increase air...i believe at this point i'd drop the needles a notch and see what happens.
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on August 30, 2014, 03:30:23 PM: Quote from: rockiedog2 on August 30, 2014, 01:49:43 PM
when doing a full throttle static runup does the motor continue to respond to increasing throttle all the way to wide open(slide all the way up) or does it top out at say for instance 3/4 of the slide range? in other words...you know on the throttle lever or handle or whatever you have where full open slide is...open the throttle up and see if max rpm is reached before reaching the full open slide position or simultaneously reaches top rpm and full throttle lever movement.
what we're trying to eliminate with this is if the carbs are too big for the motor or not. i know folks have run 28s on similar size and smaller motors and even 32s or so. but i don't know if those same folks are running egts and trying for max tune. they may be somewhere way short of max power...as far as i know we,ve never seen info to that effect on the Eaglers forums. on the mikuni app chart i think the 28s may be above the recommended size for your motor but check me on that. on that same chart IIRC 28s are indicated for the 45 and even 26s.
you got them within about 100F of one another and thats fine at this point...now you either gotta reduce fuel or increase air...i believe at this point i'd drop the needles a notch and see what happens.

Are the EGT readings stable enough now to check for n o t being on the lean side of peak ? ? ? Lower jet # should be showing higher temp if still on rich side of peak...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 30, 2014, 04:22:38 PM: Ran up again after replacing rotor and cap. Same results 950 -1000 on both sides. I am going to have to check the throttle travel vs power issue tomorrow. As you say the 28 is really too big for the 37 hp per the chart but guys fly them so I went with them. Odd to me guys were flying the 32 and making it work thought the 28 would be worth trying. The temps come up fairly equally on both sides and go down quick when throttle is reduced slightly. I have not run up with the needle clip on slot 2 yet. Has been in the middle. I will try that tomorrow and check at what percent of throttle throw I get full power.

Steve I do not know how to answer your question about stable temps and being on the lean side of peak. Can you explain please?

Thanks for all the coaching on this. Crazy business not been down this road before
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on August 30, 2014, 07:19:43 PM: Quote from: Bob Wood on August 30, 2014, 04:22:38 PM
Steve I do not know how to answer your question about stable temps and being on the lean side of peak. Can you explain please?

Thanks for all the coaching on this. Crazy business not been down this road before
Bob

The EGT temps plot as a Bell Curve - if you are rich the temps go up the curve as the smaller jet sizes lean the mixture and at peak a smaller jet will start the temp down the lean side of the curve... Therefore, as we really haven't got any plot of temps v jets sizes I'm wondering where you sit on the bell curve - if you put a smaller jet in and the temp goes up then we are making the proper jet change... The temps you have been reporting are far from the power making temps 1300 - 1400 F (could you be deep on the lean side of the curve - the 28's I have came with a 200 main jet?)....
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on August 30, 2014, 07:25:22 PM: 28 Mikuni's worked very well on my 92x69 halfVW... and working excellent on my 92x78 engine right now!
I am not real sure what size my jets are, but I am thinking they are smaller than what you are using!
I'll go look and report back.

My EGT's are 1350-1400 with CHT's around 350 at 3450-3500 RPM Max.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 30, 2014, 09:36:01 PM: Bob. You have exactly what to am shooting for. My 28 came with 200 jets. It is possible I missed the correct temps and am on the lean side of the curve as Steve brings up. It is just so odd that my plugs were so sooty and rich. I am really anxious to see what jets you are running. The other thing I am interested in is what slot your needle clip is in.
Thanks much!
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 31, 2014, 05:39:09 AM: my 45 with 28s and 200s was way rich...went all the way down to the current 150-160 to get it right. judging from that i don't think youre LOP yet especially with the sooty plugs and it being a 37.
Bob where are your needles?
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 31, 2014, 08:27:41 AM: Joe
Both my needle clips are in the middle notch #3
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 31, 2014, 09:42:25 AM: ok
i was wondering where Bob S's are.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on August 31, 2014, 09:55:22 AM: He was going to check his jet sizes and needle position I am very interested to hear!!
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on August 31, 2014, 11:24:05 AM: Quote from: rockiedog2 on August 31, 2014, 05:39:09 AM
my 45 with 28s and 200s was way rich...went all the way down to the current 150-160 to get it right. judging from that i don't think youre LOP yet especially with the sooty plugs and it being a 37.
Bob where are your needles?
I mentioned this previously in this thread but will bring it up again.

Be careful about drawing conclusions based on sooty plugs. The plugs in my Lycoming O-320 were always a tasty grey while burning 100LL avgas, but when I switched to car gas they went sooty. Jetting didn't change, performance didn't change, but the color of the plugs certainly changed.

However, you can hit the sooty plugs with a shot of brake cleaner and the soot is immediately removed and the true color of the plugs is revealed. My Casler 45 has always had sooty plugs and exhaust stacks and this is a known result of using car gas. But a shot of brake cleaner reveals healthy tan plug insulators.

I know this goes against old-school motorcycle jetting theory (been there, done that), but don't pin your entire jetting efforts on plug color. Mapping EGT will be much more productive. But even then don't blindly accept absolute EGT temps. You are looking for mapping based on "relative" temps because the numbers can vary from one engine to another due to different gauges. 1400F on one engine might be the same fuel mixture as 1250F on a different engine due to variations in gauges, probe location and turbulence in the intake tract.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on August 31, 2014, 01:32:15 PM: right. i agree. mine run sooty too always have on cargas and the stacks too. the Lycs and Continentals too...all of em.
maybe the plugs are a confirmation maybe not can't tell from here...the plug in the lean cylinder was lighter color than the richer(or lower egt)one.
but both his egts are so low that looks like a valid indication to me; regardless of plug color. and the jet/carb sizes seem to indicate it may be rich yet. guess work w/o being there.
looks like he's gonna find it whatever it is...
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on August 31, 2014, 02:47:51 PM: Here's a pretty clear article on tuning the Mikuni: http://www.iwt.com.au/mikunicarb.htm (http://www.iwt.com.au/mikunicarb.htm) How they go at it Down-Under...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 01, 2014, 05:26:08 PM: Good info in that article Steve thanks,
Joe,getting back to your earlier post. I marked my throttle throw on my quadrant and found the top 1/4 of slide opening is really doing nothing. My rpm maxes rout at about 3/4 throttle. This is with the needle clip moved from the middle position to number 2 slot. I ran it up this way with the same mains in from previous run up and got about the same EGT temps 1000-1050 in both sides. It seemed to me I got more rpms in the last 1/4 throttle with the needle clip in the middle on my previous run. Does that make sense?
Should I go back to the middle clip position and continue to decrease jet size and try to raise temps?

Still very interested in what clip position and jet sizes Bob S is running in his 28's

Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on September 01, 2014, 06:09:21 PM: SK has more knowledge on this particular thing(carb too big which is what it sounds like you have)than i do but the way i understand it is the smaller motor can't suck enough air thru the carb to use all the venturi(air) thats available so you're getting the fuel metered by the jet size but not the air. yeah it will run "pretty good" but not max performance which is what youre after. i would probably continue to go to smaller jets still and see what happens and move the needles from mid to down back and forth to see what happens but i wouldnt move them up. even tho the manual says the needles control the mid range and the main jet the upper range in my experience each seems to affect the other...it was trial and error for me when i got into that. i would also be thinking about smaller carbs
i messed around with mine for a couple months. keep at it.
just cause youre not getting 1300 egt doesnt mean you can fly it...many(most?) are too rich. (the general thinkng is it' s the static rpm that determines go no go). that involves your personal judgement of what you got...prop, gross weight, max static, runway length available, obstacles, wind temp, pilot proficiency...all those critical factors that only you can evaluate.
have fun. be careful.
Title: Re: Dual mikuni's 28's running rich
Post by: rockiedog2 on September 01, 2014, 06:11:49 PM: >>>ust cause youre not getting 1300 egt doesnt mean you can fly it

should have said doesn't mean you *can't* fly it
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 01, 2014, 06:26:27 PM: Quote from: Bob Wood on September 01, 2014, 05:26:08 PM

Should I go back to the middle clip position and continue to decrease jet size and try to raise temps?

Thanks,
Bob
Bob:
Put the clips in the middle slot and continue putting smaller main jets in if the EGT temp rises...
Steve
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 01, 2014, 06:43:31 PM: Ok thanks Steve I will continue.. I have a 110 and 115 jet coming this week to try,. Is it a good idea to use a carb sync gauge of some kind to even out these 2 carbs so they are working together? I used a carb suction gage when I first put on the carbs to set idle evenly on both and double checked that the slides were equal. Is that enough?
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 01, 2014, 07:26:55 PM: Quote from: Bob Wood on September 01, 2014, 06:43:31 PM
Ok thanks Steve I will continue.. I have a 110 and 115 jet coming this week to try,. Is it a good idea to use a carb sync gauge of some kind to even out these 2 carbs so they are working together? I used a carb suction gage when I first put on the carbs to set idle evenly on both and double checked that the slides were equal. Is that enough?

At the beginning just setting the slides so they open at the same time is adequate... Tim Floyd built a dual manometer on one board to do the WOT & 2000 rpm adjustments after he had a few hours on it - his engine revs smoothly and pulls strong... I think he ended up just balancing at idle and WOT... Tim has the TM28 carb which is designed to perform better in the mid slide ranges...

Have you stabilized your carbs with the Homan brace or is your engine a cut case?... The carbs must not be vibrating...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 02, 2014, 06:51:09 AM: Steve,
Thanks I did see the Floyd info a while back I will build one makes sense...
I have not braced my carbs yet sort of played with it and tried a stiffer intake hose but still shaking and venting a small amount of fuel at random times during the run. I was hoping as I got the engine tuned between the two carbs it would smooth out. I also was thinking as those carbs shake the float bowl needle is bouncing all over causing more fuel in the bowl than needed possible causing a rich condition I am seeing and also the fuel venting issue. Am I right? I will get back to the bracing I did see his pic ,looked better than my idea of running braces from the carbs to the bottom drilled holes on each corner of the case. Did you suggest the cut case does not have the shaking carb issues as bad.

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 02, 2014, 08:07:54 AM: Quote from: Bob Wood on September 02, 2014, 06:51:09 AM
Steve,
Thanks I did see the Floyd info a while back I will build one makes sense...
I have not braced my carbs yet sort of played with it and tried a stiffer intake hose but still shaking and venting a small amount of fuel at random times during the run. I was hoping as I got the engine tuned between the two carbs it would smooth out. I also was thinking as those carbs shake the float bowl needle is bouncing all over causing more fuel in the bowl than needed possible causing a rich condition I am seeing and also the fuel venting issue. Am I right? I will get back to the bracing I did see his pic ,looked better than my idea of running braces from the carbs to the bottom drilled holes on each corner of the case. Did you suggest the cut case does not have the shaking carb issues as bad.

Bob

Bob:
If the carbs are vibrating around the engine will never run right - brace the carbs at the air filter side using the Homan example on full case engines - the cut case engine by design dosen't have the aft case flange to anchor on - the brace for a cut case can look like the rigging Joe Spencer has but don't try doing something anchored from the engine mount - it'll vibrate worse... 1/2 Vw's shake - a good balance job makes them better - soft engine mount bushings are essential - the Balance Master disk a plus - a dynamic engine/prop balance job the final touch...
Steve
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on September 02, 2014, 09:09:36 PM: OK...So I finally got out to the hanger to inspect my LE Better-Half Mikuni's...
I was totally flabberghasted to see what I saw when pulling the jets... I don't know how or why but I have a 180 jet on one side and a 120 jet on the other! THAT sounds TOTALLY screwed up, I know, but the bugger is running just fine! NOW I am at a quandary to know what I really should have in it! I THOUGHT I was running 140 or 145's...... I guess I need to do some more testing.... One side LEAN and the other RICH????? but both sides running just under 1400 EGT's....only have one CHT and it is on the #120 side and is running 350 or so...
BTW, Both needles are set to the mid-ring...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 03, 2014, 09:04:40 AM: Bob,
Many thanks for this. Are you running Carb supports to eliminate the vibration. I put them on last night per Steve K recommendation and ran it up and I noticed a couple of things. The EGT temps seemed to come up faster and were more stable on my LED Belite gauges. I am currently at 950 and 1150 EGT with 120 and a 115 jets. Needle clips in center slot. The other good thing is all the weird air spaces and bubbles in my fuel lines to the carbs after the split have gone away. I never liked to see the air in the fuel lines!!! The vibrations must shake the hell out of those carbs and disturb float bowl operation etc.....

Do you remember how many jet sizes it took you to get up those last 200 degrees? My One CHT probe barely hits 250 during these run ups. I am turning a TN 54-22 prop and getting 3100 Static. Does that static go up a little when flying? I am running 2.3 QTS and only see about 125 degrees oil temp on the ground during my test run ups. I have hot flown yet. My Mosler 37 has a compression ratio of 8:1 after I lowered it from 9.2:1. It runs and starts beautifully with the 009 dist set up. I have a couple lower jets coming this week . Going to run up a 105 & 110 and see where I get to on EGT.

Thanks for your help, nice to have a similar power plant to discuss. this is my first Ultralight and VW project. Been flying a Tripacer for 28 years, having a ball with this, really excited to get it in the air!!

Bob W.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on September 03, 2014, 12:02:49 PM: I am NOT running any carb supports but am using a pretty stiff & short diesel heater hose for the coupling between the carb and head. I may have a MAX 1/4" between the intake and the spigot of the carb. and my intake tubes on the heads are pretty short too...MAX 2" from the head. I have black fuel lines between the pump thru the "T" to the carbs so I don't see any air there.... ONLY in the blue clear tube from the tank to the pump and that goes away pretty quick.

What jets DO you have...120 & 115 now in the carbs and what others have you tried? I have a stash of smaller jets but they were all too small!!
Carbs COME with 200's (IIRC)...and they weren't too far off really... Like I said, I THOUGHT I was at 145's before going to Reklaw....Don't suppose someone changed my jets as well as re-timed my distributor do you???

I don't really bother too much with CHT unless you are getting too hot...with all that oil, you shouldn't be too hot. I barely run 2 qts plus a 1/2 for the filter.

I liked the TN 54-20 and my BEST was a 54-22 I had cut down to 54-20!!! It had the smaller hub too... I ordered a NEW 54-20 from TN and they sent a WIDE, THICK HUB stick that was terrible! I also liked a thin 54-20 from Culver...but the prop I have from Performance is the best of the best!!!!

If your engine is newly built, all the numbers will change every time you run it until you get 25-30 hours minimum! And then they all get better from there...

I was terribly disappointed on my thrust numbers at first, but you will be surprised how even they come up. If you have a good runway area, I suggest getting it out on there and make some runs up and down. Get a "FEEL" for the T/O speed/rpm... There are those who don't approve of 'Crow Hops' but I taught myself to fly doing them! Just remember where the end of the runway is. If you can't get it back down smoothly before the end, Guess what? You better fly it!
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 03, 2014, 12:49:13 PM: Bob,

I tried extra stiff hoses also and still had vibration....My supports go from the air filter side to the corner of the case (metric threaded hole there on all 4 corners. I went just from the back hole on each side of the engine to the carb back with 3/8 aluminum tube...

My VM28's came with 200 jets and I went to 170- 145- 130- 120 now hovering at 100- 110. What happens if you go too low? do you not get the full rpms or do temps go above 1400?? I did not even see anything above 900 degrees until I but the 130- 120 in. (My #4 was a little richer than the #2)

Still get some spitting out of the carbs so I ran both vents to an aluminum tube discussed in the forum to take the venturi effect out of the equation. I still wonder if my floats are set too high....Did you adjust your float levels?

So does your static on the ground match your flight WOT RPM? What size is your performance prop? What does it pull for static? I ended up with the TN 54-22 per Scott and Leonard at Airventure last year. 3100 static was the magic number according to them.

My motor has about 50 hours on it, I put another 5 on it taxi and running up with these carb issues, feels good, and familiar. My airport has over 5000' so I was going to do some hops on calm nights to feel it out. going to be strange taking off below 60......

Thanks for the feedback

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on September 03, 2014, 01:49:36 PM: Quote from: Bob Wood on September 03, 2014, 12:49:13 PM

What happens if you go too low?

Generally your temps & RPM's go DOWN as you go leaner as well as going richer.... going Lean is quicker than rich, IIRC. Think of the bell curve. TOO Lean and it quits running, Hard to start too.

I failed to do as I am telling you: Keep a chart of CHT/EGT/RPM for each test jet... If you do that you can SEE things happening albeit very small. AND if you are doing it all static, put your THRUST values in there too... My values were all over the place.. I just had to settle on one and use it. HOPEFULLY you won't get the 1400 EGT...not right away...

You say 'spitting'....is that out the venturi? I had fuel coming out the overflow tubes and yes, I had to adjust the float levels quite a bit as the floats do pound up and down a bit! I set it so the tabs are pretty level with the bottom of the carb body.

Quote
So does your static on the ground match your flight WOT RPM?

My "static" is lower than WOT in flight but only by about 200 RPM or so. Prop unloads in the air somewhat.

Quote
What size is your performance prop? What does it pull for static?

I BELIEVE it is a 58-22 in Frank's way of measurement... Each prop mfg. has their own way to measure. I never really measured static on the PP.

Quote
I ended up with the TN 54-22 per Scott and Leonard at Airventure last year. 3100 static was the magic number according to them. My motor has about 50 hours on it, I put another 5 on it taxi and running up with these carb issues, feels good, and familiar. My airport has over 5000' so I was going to do some hops on calm nights to feel it out. going to be strange taking off below 60...... Thanks for the feedback Bob

Well, you will definitely get more RPM with a smaller pitch prop (54-20) your top speed will be less. But we arent really looking for SPEED...
anything over 3100 RPM is a bonus! I start my T/O run open all the way at 3250..climbing at same then level off at 3400-3450 before throttling back to 3300, where I cruise at 55-60 IAS It WILL take-off at lower RPM, I just like to feel the surge and clear the trees at the end of my field. I get to 100' AGL by half our 4000' runway and up to 200' by the end if everything is working well.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 03, 2014, 02:07:49 PM: Thanks Bob will keep in mind and have been charting..by spitting I mean overflow tubes. I had one spitting worse than the other so I set it to the one that spit less, since I did not have a float measurement to go to. My tabs are not level they are down a little when you look from the side not parallel to base plate. so they are leaner than yours I think if I am looking at this right. ( little tab down closer to needle means faster shut off which is leaner right??

Maybe I can go a little more lean on the float level... I will work on temps first

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 07, 2014, 06:20:43 AM: Bob. S. Question for you. All my testing and running so far has been with 91 mogas. (Eth free)Are you burning 100ll or mogas. I was thinking my low EGT may have something to do with that. I burn it in my tripacer and get 1400 no problem so no issue I keep thinking maybe vw different

We discussed float tabs & float level does being too high add to fuel spitting out overflow tubes? If you are too low I assume engine would loose power at High power settings. When I look at my float plate from the side my tabs are just the slightest down (toward the float needle). Seemed leaner than yours (being level)

After I put my carb braces on I kept going down from 120 to 110 to 105. When I hit 105 the engine loses power at about 3/4 throttle. So too lean I assume. Temps still not over 1050 So I went back to a 110 and 120 and see temps of 1000 -1050max in both sides..

Then I put the 140 and 130 back in just to see if the carb bracing changed anything and got no EGT. On either gauge. My LED gauges start at 900. I even put a 140 and 150 in to see if I was on the wrong side of the curve and again less than 900. EGT.

So...the only other thing I have not tried is moving the needle clip I notch richer. I think I mentioned I tried one notch leaner and it lost power just like when I put in a 105 jet...if moving just one notch leaner killed it maybe I am just too lean at the needle.....

So I am going to try that today. Go richer and try the jets again 120 - 180

Any chance this low temp issue is due to timing or valves. I set my points at .020. Plug gap ar .035, timing at 0. Valves .006Per Leonard. I set my timing with a light gun at 0 and checked that I do get the advance at 2500 rpm or so

I have not rechecked my valve lash since my run testing (8 hours) everything else rechecked.

Thanks for any input.
Bob Wood
Title: Re: Dual mikuni's 28's running rich
Post by: Tom H on September 07, 2014, 07:03:09 AM: Bob, you mentioned timing. I wonder if the advance is not going as far as you think. I set my timing, on both distributor and magneto, with a timing light. It gets a little windy, but is doable. At higher rpms, say over 2500 rpm, the timing is set to 28 BTDC.
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on September 07, 2014, 07:15:17 AM: Bob,
Are you sure that EGT gage is Kosher..? What brand is it, and is it new..?

There are J and K types of thermocouple probes and they must be a certain distance down the exhaust pipe from the valve seat, and reside in the center of the flow. Are the probes the same type, the right type for the gage, and in the right place..? Polarity correct..?

If there is any doubt on these questions, perhaps you could take the whole EGT package to another engine with a known good EGT setup and compare the readings you get..? This would eliminate a variable in the simultaneous equation.
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 07, 2014, 09:22:42 AM: Bob:
I think it's time for you to try a prop with less pitch - see if you can borrow a thin tip 54x20 from some one in your area or the woodbar dyno from Les Homan if you have the the 3 1/8" bolt pattern (Les may have the 4" pattern in the dyno too now - ask if you need the 4" setup)...
Steve
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on September 07, 2014, 09:29:26 AM: Quote from: Bob Wood on September 07, 2014, 06:20:43 AM

So...the only other thing I have not tried is moving the needle clip I notch richer. I think I mentioned I tried one notch leaner and it lost power just like when I put in a 105 jet...if moving just one notch leaner killed it maybe I am just too lean at the needle.....

Like Sam said the 2 strokes are very sensitive to air/fuel ratio, and die easily when it is not right. So their carbs are fine tunable. We are basically using a 2 stroke carb here, so it is very finely tunable over a very wide rpm range.

So we must keep the big picture in mind when tuning it. First and foremost it must not only be in the ball park... it has to be in the infield --before it is going to respond well to fine adjustment. We must have the floats right first, we must have the shaking out first. If the fuel is frothing... it ain't gonna run right.

Best way to get to the infield is start tuning at wide open throttle, and work your way down. WOT is main jet only... nothing else in the carb affects it, get the best (highest) rpm and plug color reading until you have the main jet nailed down. Then worry about the needle setting and if you need another needle jet.

Put a new plug in one cylinder, fire it up, run it wide open... kill it while at max rpm, read the plug. What ever the plug tells you, make that main jet change on both carbs. Rinse and repeat.

You may want to get hold of some avgas to make the plug reading easier. Here is plug reading info. (http://www.4secondsflat.com/Spark_plug_reading.html)

Or you could try a google search on plug reading with unleaded (https://www.google.com/search?q=tuning+with+plug+color+on+unleaded+fuel&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb)
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 08, 2014, 09:26:10 AM: Tom H,

I set my points to .020 at tdc, fired it up and set it with the light to Zero degrees, and it was getting to the 28BTDC mark on my hub at around 2200 to 2500 RPM

Is the the correct way to do it. I realize that if you reset points you have to re time.
Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 08, 2014, 09:56:35 AM: As i said I was going to run up with the needle 1 notch richer. It ran rough and choppy as I got to 3/4 throttle. really bad.
I did that with the 120 and the 115 jet in that gave me the highest EGT temps to date when I was at the middle clip setting. See chart below

I charted my egts on both cylinders with the needle clip in the middle.

My Belite LED EGT/CHT gauges start at 900 degrees and the lights go up every 50 degrees. My probes are both 2" below the flanges. Through all the run ups my CHT is between 250 and 300. I only have 1 side probed.

#2 200   less than 900
      170   less than 900
       150 less than 900
       130 950    ( first time the gauge showed an increase)
      120   1000   I thought I was getting there.....
      115    950 This was after I braced the carbs
       110   950
       105   bogged down and lost RPM at 3/4 throttle

#4    140 less than 900
        130 1000
        120 950-1000
        120 1050 after the carbs were braced picked up 50 degrees
        115 1150
        110 1150
        105 1050   bogged down at 1/2 to 3/4 throttle like #2 did.

my static RPM are always about the same 3090 to 3150 hard to tell above 3000 on the tine tac A2 but I checked it with a digital hand held. The only big reduction was with the 105 jet with the big cut out at 3/4 I am assuming lean cut out.

Not sure where to go from here......I thought my 3100 static was good on the prop? In the air it will be 3300 maybe......

Still wondering if my floats are set too rich.....

Maybe run 100ll and see what happens my engine is 8:1 compression I am running 91 no ethanol )

Thanks for any pointers

Bob W
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on September 08, 2014, 06:44:37 PM: Bob,
I bet you are going to wind up with something very close to 180s in both carbs and the needles in the middle. That is after you get the floats set according to the factory dimension, and a 54x20 or finer prop on it. It sounds like it is bogging from being over propped...

Where is everybody that has ran this setup..? Chime in...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 08, 2014, 09:24:24 PM: Dan , Where can I find a factory spec for float level for a vm-28 on a 37 hp 1/2 VW? I have not been able to find a thing...

I had always heard 3100 static was the place to be. I suppose cutting down the 54-22 to 54-20 would get my static up around 3400 maybe? 3600 in the air when unloaded.....
Title: Re: Dual mikuni's 28's running rich
Post by: s johnson on September 09, 2014, 06:17:46 AM: I was running 170's in my Vm28's and clip in the middle slot when I was running dual carbs on my other engine. Also using a Tennessee 54x20 prop. My egts were a little low also and could have went a little leaner but was happy with the climb. Static was around 3350. The engine just leaked oil like an old Harley. Actually worse.

Scott J.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 09, 2014, 09:08:08 AM: Hi Scott,

Sounds like where I want to be. I am getting 3100 static now with the 54-22 TN prop. How did you set up your float levels? did you see less spitting out of the vents when you leaned out the float levels? What EGTs did you see?

Do I sound over proped to you?
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 09, 2014, 09:16:00 AM: Bob S.

Prop question: in your previous reply you mentioned a great TN prop you had was a 54-22 cut down to 54-20. did TN Props just shave it down to re pitch to a 20? Sounds like I may be on that path.....

Bob Wood
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on September 09, 2014, 01:18:01 PM: Yes, Woody... I would go that route if I were you!
It's pretty reasonable, too!

Bob S
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on September 09, 2014, 04:42:23 PM: Quote from: Bob Wood on September 08, 2014, 09:24:24 PM
Dan , Where can I find a factory spec for float level for a vm-28 on a 37 hp 1/2 VW? I have not been able to find a thing...

Attached...

Make the float arm parallel to the gasket mount surface... Done.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 10, 2014, 09:12:54 AM: Dan,
Thanks for this, I did see this and set up accordingly. I thought maybe the L Eagle guys had a different setting....

How did you measure your engine thrust. I am thinking a 200# deer scale with a hook and rope tied to a trailer hitch or tree??
Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 10, 2014, 09:31:23 AM: Quote from: Bob Wood on September 10, 2014, 09:12:54 AM

How did you measure your engine thrust. I am thinking a 200# deer scale with a hook and rope tied to a trailer hitch or tree??
Thanks,
Bob

I was on dirt always and had two 4x8 sheets of plywood to put length wise under the mains & prop to prevent FOD action thru the prop... The plane was leveled up by the top fus longeron... The scale was anchored to a post level with the tailwheel spring towline connection...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 11, 2014, 03:36:40 PM: Thanks Steve, will get on that shortly I have a plan.

You mentioned the balancemaster disk a while back, I looked on their website, very interesting. Saw a couple planes in our group with them.

I have the Mosler counter balance weight on my motor, since the balance master device disk is cup shaped my counter weight would have to clear the outer edge. The plane I saw it on had no aluminum prop ring over the balance disk. If I did it that way my counter balance would not clear the balance device. I assume this thing will not take the place of the counter balance. Have you seen these mounted with the 1/4" prop ring over the device? If I did that I think it would fit fine.

Thanks for input, I am going to give them a call tomorrow,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 11, 2014, 03:45:51 PM: Quote from: Bob Wood on September 11, 2014, 03:36:40 PM
Thanks Steve, will get on that shortly I have a plan.

You mentioned the balancemaster disk a while back, I looked on their website, very interesting. Saw a couple planes in our group with them.

I have the Mosler counter balance weight on my motor, since the balance master device disk is cup shaped my counter weight would have to clear the outer edge. The plane I saw it on had no aluminum prop ring over the balance disk. If I did it that way my counter balance would not clear the balance device. I assume this thing will not take the place of the counter balance. Have you seen these mounted with the 1/4" prop ring over the device? If I did that I think it would fit fine.

Thanks for input, I am going to give them a call tomorrow,
Bob
Mine runs under the prop crush plate on the front side of the prop - think Scott Johnson has his mounted that way too... BTW: I have a Prince UL prop 54x20 with a 4" bolt pattern - I'm going to the shop tomorrow - is that something that would work for you?... The prop has never been taken out of the box - I think it's in there... Long story on that...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 12, 2014, 09:24:10 AM: great I am going to do the balance master.
I have to check now but Scott Casler called my mosler the large hub..My prop has the 2" counter bore pilot hole.
I have to check to see if the spacing was 3 1/8 or 4"
Yes I may be interested in that prop if it fits.

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on September 12, 2014, 12:02:33 PM: Quote from: Bob Wood on September 12, 2014, 09:24:10 AM
great I am going to do the balance master.
I have to check now but Scott Casler called my mosler the large hub..My prop has the 2" counter bore pilot hole.
I have to check to see if the spacing was 3 1/8 or 4"
Yes I may be interested in that prop if it fits.

Bob
One of the cardinal rules of engine troubleshooting is to only change one variable at a time.

Wouldn't it be best to get the carbs straightened out before considering other stuff like balancers? Uneven carburetion can play havoc on engine smoothness.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 12, 2014, 12:55:55 PM: Well said Sam, I am going to finish the carbs before I put on the balancer and try a different prop. I reset the float levels and ran up earlier in the week and I saw my temps pop up faster on the LED gauges, i had my 120 and 115 jets in and when I hit 3/4 throttle it was cutting out. That never happened before unless I had the 105 jet in one side..... I had 1 float low and the other higher than the book....So I am going back to the larger jets and looking at temps again. Seems like I am almost there...I would assume now I am on the lean side of peak on that bell curve....When I get my temps up around 1200-1300 I will do the thrust test. Waiting for the rain to quit and the temps to get over 50!!

Want to get this bird in the air before the snow flies, which may be soon in Wisconsin!!

Thanks again for the pointers!!,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 12, 2014, 01:16:59 PM: Steve K,

My Mosler hub is a 6 bolt 3 1/4" hub with the 2" counter bore. Thanks anyway if I get to that down the road maybe somebody in our group may have one. I am finishing the carbs before I do anything else. I think I am close...

Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 21, 2014, 11:39:31 AM: Update:
After adjusting float level, bracing carbs, my jetting has changed still not up to 1200 but as high as I can get it. Here are my jets and temps
# 2. 170 Jet less than 900
155 jet. 1050
145 jet 900-950
150 jet. 1050-1100. Static RPM 3060

#4. 170. Less than 900
155 jet 950
140 jet 1000-1050
130 jet 1050-1100. STATIC RPM 3060

So finally have the 2 sides even on temps. I checked my tiny tac with a digital for max rpm and got 3060. Tiny tac was bouncing around at WOT.

Next I set up the thrust scale and at the max jets and 3060 RPM above I got 150 lbs thrust.
Am running a TN 54x22. I spoke to TN PROPS and can get a 54-20 repitch for 75.00 and 1 week wait.

If anybody has a Mosler 6 bolt 3 1/4". Prop with the 2" counterbore. I may be interested......

I am thinking more rpm may give higher EGT and also my extra thrust

Am I on the right track.?
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Steve on September 21, 2014, 12:19:10 PM: Quote from: Bob Wood on September 21, 2014, 11:39:31 AM
Update:
After adjusting float level, bracing carbs, my jetting has changed still not up to 1200 but as high as I can get it. Here are my jets and temps
# 2. 170 Jet less than 900
   155 jet. 1050
   145 jet 900-950
   150 jet. 1050-1100. Static RPM 3060

#4. 170. Less than 900
   155 jet 950
   140 jet 1000-1050
   130 jet 1050-1100. STATIC RPM 3060

So finally have the 2 sides even on temps. I checked my tiny tac with a digital for max rpm and got 3060. Tiny tac was bouncing around at WOT.

Next I set up the thrust scale and at the max jets and 3060 RPM above I got 150 lbs thrust.
Am running a TN 54x22. I spoke to TN PROPS and can get a 54-20 repitch for 75.00 and 1 week wait.

If anybody has a Mosler 6 bolt 3 1/4". Prop with the 2" counterbore. I may be interested......

I am thinking more rpm may give higher EGT and also my extra thrust

Am I on the right track.?
Bob

You are on the the right track and the prop change expectations are correct on thrust and EGT...

From collected reporting on props:

The de-pitch change you are considering on the Tennessee 54x22 will yield an additional static 150 rpm and 100 degrees more EGT...
Leonard shortened the 54x22 prop on his Dual Mikuni version of the Betterhalf prototype to bring the engine (alive) - his cut prop was 52x22... The engine 69x92 well run-in...
Frank Johnson has experimented with a 52x22 prop that users report out performs the 54x22's they were running... Frank has modified his blade layout on the 52 and that is important to note...
The advantage of leaving the pitch at 22 is once you are in cruise the rpm required will be less... Generally the draggy airplane flys best with the longest prop you can turn up to rated rpm...

My 69x94 engines turned 3100rpm EGT 1300 static when fresh on a Peery 54x24 prop (very thin blade shape) the LE climb at 525 lbs gross was underwhelming... Changed to a Tennessee 54x20 prop the engine turned 3350 rpm EGT 1400 static and ROC went into the 400 ft/min range ...
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 21, 2014, 07:45:20 PM: Ok thanks for the prop reports. Do you think the repitch to 54-20 will get me from 150 to 170 thrust.

Is 150 too low to safely fly the XL? I have not head many reports on thrust measurements and what is really go or no go.

Thanks Steve
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Tom H on September 22, 2014, 07:38:37 AM: Bob Wood, be careful, max static thrust is not the "final answer" as to how the airplane will climb or fly. Static thrust tells you the prop's performance at zero airspeed. It may indicate how quickly the airplane will start accelerating on take-off roll. But, as soon as you get some airspeed, the prop may or may not be doing as well.

We just tested a new, beautiful Performance Prop on our DE Stubby. A work of art. We got the best static thrust numbers yet, with higher rpms (about 3400) just like we wanted. It accelerated quickly, broke ground sooner, but did not give us much better climb than our main prop (3100 static). And, in level flight, I did not get to full throttle because the rpms hit red line. Also, had to run the engine about 3200 to get the same cruise as the old prop would get at 3000. That was expected, but, increasing rpm on up to 3600 did not yield much gain in speed. Seems the prop hit its limit. Probably pitched too low.

So, Frank says to send it back and he will make some pitch tweaks to it, which, I hope, will put it somewhere between our main prop and the tested PP prop, yielding better climb, but only a slight loss of cruise speed.

I think, for best climb, the prop needs to be just slightly stalled at zero airspeed (which give high rpms, but not high thrust numbers), then un-stall as airspeed starts to pick up, maybe just before lift-off/climb speed, at the target rpm.

Maybe the best test would be to tow the engine/prop on a test stand at 50 mph and measure the thrust in that condition. Somebody should work on that. Should make a good video.

That's my thinking, anyway.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 22, 2014, 09:26:43 AM: Tom,
Interesting, I think I am going to do more high speed tests and maybe a take off or 2 on my 5600 foot strip and see how it goes. Does my 150# seem low at 3060 static? In actual flight when the prop unloads I would expect to gain 100-200 RPM and the thust that goes with it. So I may be ok??

I would rather order a new prop and have the ability to go back to my 54-22 that cut mine up. I am running out of WI summer is there is such a thing.

I have about 11 hrs in run and taxi testing on my motor that has about 50 hours total time. I feel like it is ready to go up...
Thanks,
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Sam Buchanan on September 22, 2014, 11:21:46 AM: Skip further thrust tests, jetting tests, and most of all, the high-speed tests.

Time to fly.

No more paralysis by analysis. ;D
Title: Re: Dual mikuni's 28's running rich
Post by: Tom H on September 23, 2014, 05:40:19 AM: Bob W, Sam said it.

We built and flew a LEU (Treehugger). It was a tad heavy. The engine wood bar dyno test showed 29 HP at 3400 rpm. We had a 54x20 prop (unknown mfg), and full throttle static was 3150 rpm. It was probably developing 25-26 HP at this rpm. Static thrust was around 100 lbs. My notes say it climbed at 3220 rpm. I do remember that climb was very poor, though. But, it flew, and we flew it, but decided it needed more HP and less weight. Stopped all development work when it met up with a tree. All OK, airplane in pieces in storage.

You have a nice, long runway. Almost a cross-country in a LEU (except for Les Homan). If you have the basic airplane flying skills, and if the airplane has a flying CG at 28 - 30% of wing cord, you should be able to fly it. If you have decent altitude half-way down the runway, keep flying. If climb was pathetic, you have half a mile to land.

On landing, with power at idle, our LEU had to be pointed toward the ground, as compared to any conventional airplanes that I have flown. It seemed weird, at first. You want to keep airspeed up until you are close to the ground before flaring.

Pick a calm day. Fly the thing. Have fun. Have someone shoot a video.
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 23, 2014, 08:03:20 AM: ok, sounds good to me, I did a test hop last night flew a portion of the runway . Slight crosswind and the sun was down so I called it a night. Tail popped up jumped right off , seemed smooth and stable.....Good weather next couple of days, will advise how it goes.

Thanks for all your help!! My worst fear was not flying it before winter.....

Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Bob S. on September 25, 2014, 08:55:58 PM: Just FYI, I pulled my jets again and I know I SAID one was a 120...well, I just checked and it is MARKED 120 but I drilled it out to match the 180...so they are in essence both 180 jets and the needle is in the middle slot. My EGT's are just under 1400 and CHT on the one head is around 350....

Sounds like you are getting yours narrowed down! AND getting some air under those wings??
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on September 29, 2014, 05:17:57 PM: Bob S.
Thanks for this info I still have jetting work to do but I did get 3 flights in and have it running well at 1150 or so on both jugs an a 130 and a 150 jet.

These are a ball to fly, I jumped off and flew at 3/4 throttle the length on my 5600 ft runway at about 50 ft or so and had great control and stability. I did have rigging issues which I am starting a new discussion on. Please jump in .

Thanks to all of you guys for getting me into the air!!
Please jump into my rigging thread
Bob
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on October 11, 2014, 04:25:47 AM: Quote from: Bob Wood on September 10, 2014, 09:12:54 AM
Dan,
Thanks for this, I did see this and set up accordingly. I thought maybe the L Eagle guys had a different setting....

How did you measure your engine thrust. I am thinking a 200# deer scale with a hook and rope tied to a trailer hitch or tree??
Thanks,
Bob
Here is a good web site with tuning tips and manuals...

www.mikunioz.com/tuning_manuals.htm (http://www.mikunioz.com/tuning_manuals.htm)
Title: Re: Dual mikuni's 28's running rich
Post by: Bob Wood on July 10, 2020, 11:54:39 AM: I wanted to get back to this thread as I am ready to try to lean out my 37hp 1/2 vw. I have 10 or so issue free flights which I chalk up to no vibration shaking the float needles, making the motor run rich at certain rough power bands. It even happened when landing in a rough field where the floats bounced around and overflowed. So I am running great right now but still low EGT.

I have been running 170 main jets with the needles on the middle notch. My EGTs are around 900 on both sides. I just went to 160 mains for a couple flights and saw no change. I was going to go to 150 next, to see if I can get then up to 1000 or so.

My CR is 8:1 and I am running premium Mogas.

Comments greatly appreciated.
Title: Re: Dual mikuni's 28's running rich
Post by: Dan_ on July 10, 2020, 05:06:25 PM: This may be apples to oranges for example he is running a bigger engine with smaller carbs, but I thought it was interesting.

https://www.youtube.com/watch?v=OK9zD2LKO4Q
Title: Re: Dual mikuni's 28's running rich
Post by: Chuck in Indiana on July 11, 2020, 04:21:56 AM: Quote from: Bob Wood on July 10, 2020, 11:54:39 AM
I wanted to get back to this thread as I am ready to try to lean out my 37hp 1/2 vw. I have 10 or so issue free flights which I chalk up to no vibration shaking the float needles, making the motor run rich at certain rough power bands. It even happened when landing in a rough field where the floats bounced around and overflowed. So I am running great right now but still low EGT.

I have been running 170 main jets with the needles on the middle notch. My EGTs are around 900 on both sides. I just went to 160 mains for a couple flights and saw no change. I was going to go to 150 next, to see if I can get then up to 1000 or so.

My CR is 8:1 and I am running premium Mogas.

Comments greatly appreciated.

Ok, where are your egt pickups located? An inch closer or farther away from the exhaust valve will make considerable difference. What do your plugs look like? That is a good indicator of mixture.
Mikuni's are motorcycle carbs, and quite resistant to vibration. I have found that carburation problems are almost always ignition. :))