Gas engine tuning for newbies....

[mfuess]

	Quote: Originally Posted by khan
	please clarify. Your original article says to open the highend not the lowend. Thanks!

Khan,

I found where you saw the reference to highend and that is incorrect. I pulled up my original article and it is correct, lowend. Sorry for the confusion.

Tuning a gas engine isn't "rocket science", but there's a method to the madness. If your engine is equipped with a Walbro or similar diaphragm carb there are a few things that are consistant. You can start and run your engine with the highend needle completely closed. It won't run great, but I'll run. Of the two needles, the lowend does most of the work because it operates all the time even at full throttle. The topend only operates at just above mid-throttle and above. So, once the topend needle is peaked, it's done... the rest of the tuning will be on the lowend, which includes transition, and mid-range.

[Stainless Skills]

I recently went out to tune my engine using your method.

I let the engine warm up, set the high end and then ran it at WOT for 20 seconds and the rpm did not drop. This all took a little over a minute. Then I let the engine cool.

I then continuously leaned the low end bit by bit following the 4 stroke popping sound all the way down to just above idle. Then I let the engine cool.

The engine transitioned from idle to WOT perfectly and ran very smooth all the way down to just above idle but still four strokes at 2000-3000 and maybe even a little higher rpm. Just above idle.

I am afraid to lean the low end more because I may have already leaned it in a whole turn.

Other than that everything else is factory settings.

How do you get this 4 stroking right above the idle to go away? Do you keep leaning the low end?

[Stainless Skills]

Oh BTW, The engine still holds RPM and full throttle for 20 secconds when it is warmed up. So the low end has not leaned the high too much, yet. The "yet" is what I am worried about and is what is keeping me from leaning it more.

The engine runs great in the air, it just 4 strokes right above idle.

[mfuess]

	Quote: Originally Posted by Stainless Skills
	Oh BTW, The engine still holds RPM and full throttle for 20 secconds when it is warmed up. So the low end has not leaned the high too much, yet. The "yet" is what I am worried about and is what is keeping me from leaning it more. The engine runs great in the air, it just 4 strokes right above idle.

OK, thats a tough one to get rid of. What you are experiencing is very common. You have some choices though. You can continue leaning the lowend until the "four stroking" is gone, BUT you will have to richen up the highend slightly to keep it from going too lean. Your "other" option is to lower your float lever slightly. Of the two choices, I prefer working with the lowend.

If it's your float lever causing the off-idle "four stroking", there is a way to check this, and it's not too complicated. Completely close off the highend and start the engine. Let it warm up, and then throttle up just off idle, maybe 2500/3000 RPM. IF it's "four stroking" try to lean it out "SLIGHTLY". If the "four stroking' does not go away, the Float diaphragm lever is too high, or your check valve is leaking.

IF it doesn't "four stroke", then you can begin to open up the highend maybe 1/4 turn at a time until you regain peak power. If the "four stroking" returns, then you will have to adjust the float lever.

[mfuess]

	Quote: Originally Posted by Stainless Skills
	Oh BTW, The engine still holds RPM and full throttle for 20 secconds when it is warmed up. So the low end has not leaned the high too much, yet. The "yet" is what I am worried about and is what is keeping me from leaning it more. The engine runs great in the air, it just 4 strokes right above idle.

Stainless, Skills,

I went back through a bunch of my field notes on similar problems some people were having. In some cases, we were not able to totally get rid of the off-idle "four stroking" without doing a major carb overhaul. But, if the engine(s) ran very good overall, we left them alone. At our airfield about 98% of the gassers "four stroke" at some throttle position. It hasn't been a problem, except for those that really had a bad tune.

[Rocky V.]

Hey Mark,
Thanks for all the good info.
Is it better to do these ground adjustments with cowl on, or does it matter ?

[khan]

Thanks for clarifying!! This confused me a lot. And thanks for all you inputs!!! We should save and print them all.

[JimC-MD]

	Quote: Originally Posted by mfuess
	ALL of my Tech Site Documents get updated regurlarly with new information and new illustrations. And, I copyright them for the current year they are UPDATED. This particular document was actually written in 2005, by me. I took all those Walbro photo illusrations as well. I have ALL the original documentation and illustrations dating back to its origin in 2005, as well as the UPDATED documents. I even have the original MS Word files I created this document in. I spent 100's of personal hours creating this stuff for the benefit of all RC modelers. Especially those new to RC Modeling. I want you guys to benefit from my 37 years of RC modeling and my extensive gas engine expertise. But, I don't want anyone taking or editing my material without my permission. I don't think that's asking too much... do you? All someone has to do is e-mail me for permission to link up to a particular Tech Page and I'll furnish the page link WITHOUT the Greater Southwest Areo Modelers advertising frames. Here is the main GSWAM Tech Site address: http://tech.flygsw.org/ You can link up to my Tech Site and ALL the Tech pages YOU want! That's what its there for... But please allow me due credit for my VOLUNTARY HARD WORK for you guys.

Mark,

I hope you understand why I asked the question. This method of sharing information will raise all kinds of issues now and in the future. You obviously have a good handle on this stuff based on your comments in this thread. It is too bad that it took this issue to bring you onto the forum full bore. Welcome.

Thanks for your contributions.

[TrikeFlyer]

In your post you say to tune the Hi needle to peak RPM and NOT ot back it off 200 RPM or make richer.

I am confused as this is opposite of everything I have read on tuning a gasser. What is the reasoning behind this???

Thanks - Trike

[mfuess]

	Quote: Originally Posted by TrikeFlyer
	In your post you say to tune the Hi needle to peak RPM and NOT ot back it off 200 RPM or make richer. I am confused as this is opposite of everything I have read on tuning a gasser. What is the reasoning behind this??? Thanks - Trike

This is very simple. Your engine uses a carb that has a fuel "Pump". Regardless where the tank is located, and regardless how much (or how little) fuel is in the tank your fuel to air ratio does not change. Because it doesn't change, there's no point in having the engine run less than optimum performance. IE: rich. Your carb (when properly tuned) will maintain that same exact air/fuel ratio in the air as well as on the ground. So, setting your topend needle a little on the rich side serves no purpose, except robbing you of it's peak horsepower.

I know some people "think" it's better to run a gas engine slightly rich, but all you're really doing is creating more carbon in your cylinder, more carbon on your piston, and lots more carbon in your exhaust. Remember, this isn't a GLOW ENGINE so don't tune it as though it is.

[mfuess]

	Quote: Originally Posted by STR8HUCKIN
	I dont think you would run any engine day after day wound all they way out to it's peak unless your sponsored or just really dont care...

Peaking an engine Doesn't Mean blowing up your engine or wearing it out. It means your engine is running at peak EFFICIENCY. An engine that is "peaked" to it's best possible tune, runs clean (minimum carbon), no sparkplug fouling, and it produces the HP it was designed to produce.

I have engines that have well over 600 flights on them, and they run as good today as they did the day they I bought them. In other words; a well tuned engine runs better and lasts longer.

[mfuess]

	Quote: Originally Posted by JimC-MD
	Mark, I hope you understand why I asked the question. This method of sharing information will raise all kinds of issues now and in the future. You obviously have a good handle on this stuff based on your comments in this thread. It is too bad that it took this issue to bring you onto the forum full bore. Welcome. Thanks for your contributions.

Jim,

I just wandered into this forum and stumbled across my stuff. I stay very busy keeping my Tech Site up to date, then at the field I spend a lot of time working on peoples carbs & engines. I also evaluate new engines, and do glow to gas conversions now and then. But I'll try to visit regularly to see what's brewing here. You can always e-mail me, and visit my Tech Site.