Gas engine tuning for newbies....

[cforcht]

I want to replace the cowl and install a pitts style muffler. but Aeroworks doesnt offer the cowl. So I have to wait for stans fibertech to get into production so i can get a replacement. they are going to produce the replacement. as per my conversation with them last week. they project being in production inside of a week. (holding breath) this will help shroud the carb but what do I do in the meantime? I am pretty new to giant scale. but I am pretty handy once I have an idea of what I need to do. how shielded does it need to be? I am used to flying glow engines so I am pretty clueless to the needs of a gas engine. but I have a handle on the tuning part. thanks to this thread. I have found its quite easy in fact. especially so when compared to 90 class helis.

[Kiwi]

cforcht.

Try soldering a small brass tube onto the vent hole on your carby. That is the vent hole over the top of the diaphram. Remove the four screws, take off the plate and neatly solder the tube to it. When its cool blow through it to be sure you did not block the hole in the process. If it's clear refit it then run a fuel tube to a location inside the fuselage. Some place where you think the air will be static. See if that helps.

Kiwi

[cforcht]

now that is something that I can do quite easily. thanks for the info guys. i will let ya know how it goes. also should I remix the fuel to 40:1 or leave it at 50:1 thanks guys.

[cforcht]

Well I found something quite interesting. I went to remove the carb so I could solder the line to the diaphragm cover and discovered the high needle valve is now missing. after the last flight today I didnt even look at the engine I just packed it up and went home. So.... in light of that I now wonder if the needle valve was moving around the whole time making it run erratic. sounds like a good possibility to me since its now MIA. now that I have the carb in hand. where the heck is the model number found on these things. I do not have a walbro carb. its a tillotson carb. the next question. is this a good thing or a bad thing. would a walbro do better or should I stick with the tillotson carb?

[strulag]

I read this post to learn how to tune gas engines (I'm not that good at tuning glow ones either) but how do you know when the engine "goes lean" or "four cycles"?

[Dan767]

Your carb is either an HE or an HS Tillotson. Find a good chainsaw shop and get a needle from them. There should also be a spring around the base of the needle to keep it from coming loose.
The problem you're having also happens with a carb that is not mounted tight enough to the engine. Air leaks around the carb base where it comes in contact with the engiine will run just as yours. Great on the ground, lousy in the air. Be sure that the gasket is good and the mounting hardware tight.

[RTK]

	Quote: Originally Posted by flyfreak3
	I read this post to learn how to tune gas engines (I'm not that good at tuning glow ones either) but how do you know when the engine "goes lean" or "four cycles"?

When it goes lean it will start loosing power (slowing down/sagging) and that is not good. You should get off the throttle.
When it is "four cycling" it will make a popping sound, not a smooth steady sound. That is about the best way I can explain it. Maybe someone can do better.
While running really rich is not good for an engine, it also will never destroy an engine like running it too lean.

[cforcht]

Had to order the needle from aircraft intl. the local small engine shops didnt have the needle in stock and it was on back order from the manufacturer. had it in 3 days from aircraft intl. when I re-installed the carb I found that one bolt would not tighten up because the manifold was partially stripped. of course. when I tried to tighten it up I finished it off. I have that fixed already as well. but didnt get a chance to fly this weekend because I spent most of it working on my H9 ultimate.

I too was wondering what the "four cycle" sound was. but I have figured that one out. heres how to find that sound. richen up the needles a little. let the engine run wide open after its warmed up a bit. then lean the high needle until it sounds very smooth. if using a tach... when it maxes out the rpm. then back off the throttle very slowly until you hear it start gurgling in the exhaust. this is four stroking. lean the low needle very slowly until it smooths out. slowly lower the throttle some more until the gurgling comes back. lean the low until its gone again. keep repeating until you have the engine back to idle. you have now tuned your engine. you will have the four stroking every now and then when you abrubtly back off the throttle. but this is normal. and its very brief. its the engine burning off the excess fuel from the rapid throttle change. this method is amazingly simple. now you do have to consider that most engine manf. suggest you find the high needle setting by leaning the high until it achieves max rpm by tach then richen it up until it drops about 200-300 rpm. you do this in an attemp to make sure you dont run it too lean on the top end. if you run it lean too long you will sieze the engine. because it will overheat. hope that helps.

[krayzc]

good scoop

[Izzy]

So do you tune the carb before the very first flight? do i put it on the stand, run it and tune it, fuel it up again, and fly?

[flyingklown]

ROLL TIDE!

[mfuess]

Greetings gentileman,

The Xipp Tuning Methon is ACTUALLY my work. Here is my link to my ORIGINAL page: http://tech.flygsw.org/walbro_tuneup.htm

You'll see that I am the Author, and it's copyrighted... This page is only one of 100's of topics I've written for the betterment and introduction to new commers to our magnificent hobby.

I certainly don't mind people using this information (that's why I created it), but I'd like to get due credit for hard my work.

All of my technical publications can be found at: http://tech.flygsw.org/ including the one posted here.

I'vee been in this hobby for 37 years and a highly skilled gas engine devotee, please allow me the priviledge to see my name associated with my expertise and publications.

Best Regards,

Mark Fuess
Author
Greater Southwest Areo Modelers Tech Site