Gas engine tuning for newbies....

[JoeAirPort]

	Quote: Originally Posted by i3dm
	Hey guys, I understand the method, but im not sure im following on how a "four storking" engine sounds, can you try to explain please ? thanks.

4 cycling is a lower pitch sound. It is not combusting every power stroke so it sounds lower, also can sound like it's missing. After leaning the low end, when running at 1/4 to 1/2 throttle, it will start to fire every power stroke making a higher pitch sound (consistent pops one after another, no missing).

[BAS]

I havent been on here for awhile but thought i would pass on my tuning of my Brison 3.2 yesterday and how happy i am now that i tried Xipps method of tuning gassers. Let me just say i have had all brands of gassers for the last 15 years from Brisons , Taurus , Zenoahs . I have always had problems getting rid of the mid range burble on the motors and was always frustrated with not being able to tune them properly . I used this method yesterday and followed the procedure by the book , and all i can say is that WOW what a difference i can tell now. I tuned my Brison 3.2 by starting all over on the needles as the procedure calls for by having both needles out 1 and 1/2 turns out . After i completed the procedure in the air the motor had absolutely no midrange problems and ran really well , it is like a new motor now . I am running a MSC 22/8 prop on the Stinger 84 span and i am a happer camper now . I will retune all my gassers now including the Taurus 52 and my other Brisons including my 6.4 twin. Thanks for the info on the tuning .

[cforcht]

OK guys I tuned my 3W70 as per instructions found here. it runs flawlessly on the ground with good transition. the idle might be a tad high but otherwise runs great. In the air however its another story. it runs fine for a little while then acts like its choking on fuel and loading up. I have tried to lean out the high side a bit to remedy it but then it runs worse. same goes for richening it. but yet it runs fine on the ground. what am I missing here. fortunatley it hasnt died in flight even though now and then it sounds like it might. but it has died on the ground after landing. any ideas whats wrong?

[Neogenesis]

sounds like a pressure problem inside the cowl. How open is the bottom?



Neo

[cforcht]

the bottom of the cowl is very open. the previous owner hacked the crap out of it for the banjo style muffler. this engine starts easily. usually the 3rd or 4th flip after its popped while choked. runs great on the ground but doesnt work that way in the air. I am using redline oil mixed 50:1. I have discovered today that 3W recommends this particular oil mixed at 40:1 so that may be some of it. what ya think? would this cause it? also the carb is exposed to the air stream around the plane as it flies. there is nothing shielding it or obstructing the intake path of the carb.

[notorious_benny]

I think you are getting turbulent airflow around your carb.

You might need to protect the venturi and the diaphragm vent hole from hostile air.

[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