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RE: GMS Engine Tuning Problem - 6/25/2008 10:33 PM   
Dad_Roman



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From: Teague, TX, USA
Status: online 		I thought about that quite a bit. The needle has a slight taper to it. If you simply unscrew it, it will allow more fuel through at idle, however, at WOT the tip is recessed into the spraybar, thereby impeding clean fuel flow. By shortening it slightly, the taper contacts (or comes close to) the spraybar in the same (screwed in) position even though the actual tip (almost) contacts the inside of the spraybar farther out (obviously 1mm). However because it is shortened, the tip now clears the end of the spraybar, at WOT, which allows full unimpeded flow from the spraybar.

If you just screw it out a ways, then you dont get to screw it in if you need to lean the low end.

Im not technical about this. Im just trying to glean the sensible information off here to get my engine to run well Perhaps this wasnt needed, I also drilled out my fuel nipple/spraybar tube at the same time.

This was a recomendation of XJet. Made good sense to me. Remember what my problem was. I couldnt get the engine to run a rich 4 stroke, even with the needle out in my hand! It was obviously fuel starvation and these seemed to be logical steps to over come that in my case. And they worked, but thats me

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RE: GMS Engine Tuning Problem - 7/20/2008 12:41 AM   
hyflyer9


 

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Status: offline 		I have a gms 76 pro ringed engine and it took me about 2-1/2 weeks to get it broke in properly it now runs like a charm and it is one of the easiest engines to start that I have ever owned . run it rich for the first few runs and then lean it just a touch for a few minutes at a time with cool down time in between runs . good luck and safe flying

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RE: GMS Engine Tuning Problem - 9/13/2008 11:24 PM   
larrysogla


 

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Status: offline 		This is such a wonderfully informative thread. It is amazing in it's helpfulness and scope. I started RC glow way back in 1979 and quit in 1981 due to the expense(crashed airplanes and the distance to Sepulveda Dam Apollo Model Field, 15 miles). Now after getting back into RC via electric planes starting last year, I just had two Hobbico Twinstar ARF's with 2 Magnum .28 glow engines and the associated paraphernelia delivered to my door a few days ago. One Twinstar is going electric, one Twinstar is going glow powered and also a third I just ordered yesterday is a crash reserve. At $109 per Twinstar(no sales tax) and free shipping with my new membership plus the $25 instant discount, I came out a winner with this cheapest twin I could find on the market and the reviews say that it flies good too. I have not done anything yet due to schedule. However, I have been reading a lot on tuning glow engines. This thread by far is the most far reaching and comprehensive on glow tune-ups.
The RC 2 stroke glow engine has been around for over many decades and yet I find the material discussed in here thoroughly fascinating and eye opening. Wow!!!! the idle could be running reliably and yet be out of adjustment. As simple as pinching the fuel hose while idling and catching the slight change in RPM allows correct idle setting. Did not know that helpful tip till I read this thread. Then the interaction between the High Speed Wide Open Throttle setting could affect the idle setting and thus the need to revisit the idle adjustment and then vice versa for the High Speed adjustment until both are adjusted correctly with the transition resulting in smooth as silk action. I always thought from my days of 1979 RC glow flying that you set the W.O.T. adjustment and then the idle adjustment and that was done (I had bought brand new and flown these Super Tigre .60, OS .35 & .25 and Thunder Tigre .25 with no engine performance issues at all back in 1979-1981). Well as noted in this thread I was just lucky way back then.....because as correctly explained by some wonderful guys in this thread that there is a certain amount of interaction between the High Speed setting and the idle setting IF...IF......IF...the low speed needle is still slightly inside the tip opening of the spraybar at WIDE OPEN THROTTLE. This has the effect of restricting/obstructing the fuel flow at W.O.T. at the spray bar tip regardless of High Speed needle adjustment. This is the reason why on SOME ENGINES WITH THIS CONDITION, the HS needle is already backed out till it almost falls off and it still has no effect on the W.O.T. setting. The Low Speed needle still intruding into the spraybar at W.O.T. is effectively regulating the fuel flow even with the HS needle fully backed out. Thus the engine leaning out and quitting at W.O.T. (especially on take off with full power on and on high speed flight). One persistent fellow's solution is to look down into the carburetor throat and back out by .002-.004 the intruding LS needle tip away from the spray bar opening tip and thus remove the obstruction at W.O.T. Others have a different problem, like one fellow has misaligned fuel passageways, another has out of range glow plugs, another has too small a prop allowing too high a W.O.T. rpm probably RPM'ing out of the maximum fuel delivery calibration set by the manufacturer for that size carburetor spray bar, fuel tank installation too high, too low or too far. For me the most fascinating is the Low Speed needle intruding into the spray bar opening tip at W.O.T. thus causing a fuel flow obstruction at W.O.T. making the High Speed needle unresponsive even in some cases backed out nearly all the way. With the wealth of astounding tips in this thread, I am more and more confident that I will be able to fly those twin .28 Magnums on my Twinstar and avoid engine performance/reliability issues. You guys are wonderful, saving many, many of us from countless frustrating hours trying to fix engine issues that after completely reading this thread from start to finish makes the obvious sense. You guys deserve our appreciation and thanks. God Bless y'all.
larrysogla

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RE: GMS Engine Tuning Problem - 9/14/2008 2:07 AM   
Dad_Roman



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Status: online 		My gosh Larry...that was quite a mouthful for a third post

These issues are with the GMS engine only, and these are quite serious engineering flaws that we are dealing with here.

That being said, you shouldnt have any "performance/reliability" trouble with other engines, and certainly not like this.

Update: Mines runnin like a screamin banshee, strongest "46 class" motor I have had by far

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RE: GMS Engine Tuning Problem - 9/15/2008 4:39 AM   
Flyboy Dave



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Status: offline 		....yep. I must say, mine is running great too....

....no dead sticks....mucho power, for an inexpensive engine.

FBD.

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RE: GMS Engine Tuning Problem - 9/15/2008 9:54 AM   
The Raven



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From: Melbourne, AUSTRALIA
Status: offline 		Other than the air leak that won't let you shut them down, I've not a word of complaint about these engines.

Yes, they can fuel up at low speed but then I consider them quite 'sporty' and a little more powerful than their OS equivalents (.32 and .47 in particular). I spend my time flying above 50% throttle so it's not a concern.

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RE: GMS Engine Tuning Problem - 10/26/2008 1:17 AM   
Wayne Miller


 

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From: DrumboOntario, CANADA
Status: offline 		Hi,

For some reason I haven't been notified of the latest posts, I just thought I'd check. I found new posts and I enjoyed getting caught up with the latest comments.

My GMS's are all working great, and I'm glad to see others are able to get theirs working well and are enjoying them. The last problem I had was when I tryed to run old fuel, worked great on the ground, but died 1/2 way through flight - of course I screwed things up by trying to adjust the carb for it, but after getting new fuel and a few minor adjustments, all was well again.

I hope everyone is enjoying their GMS as much as I am.

Fly4Fun,

Wayne


< Message edited by Wayne Miller -- 10/26/2008 1:18 AM >

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RE: GMS Engine Tuning Problem - 10/26/2008 1:46 AM   
Dad_Roman



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Status: online 		Heya Wayne, I run old fuel all the time when people give it to me. Just gotta mix a little in at a time so you get the milage out of it but it doesnt upset anything

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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> RE: GMS Engine Tuning Problem
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