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larrysogla -> RE: GMS Engine Tuning Problem (9/13/2008 11:24:22 PM)
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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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