Dual mikuni's 28's running rich

[Sam Buchanan]

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.

[rockiedog2]

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.

[Bob Wood]

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

[Bob Wood]

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

[Bob Wood]

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

[Sam Buchanan]

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.

[rockiedog2]

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.

[Bob Wood]

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

[rockiedog2]

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...

[Bob Wood]

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

[Bob Wood]

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

[rockiedog2]

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.

[Steve]

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...

[Bob Wood]

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

[Steve]

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?)....