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Old 07-06-2007, 10:20 AM
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Scotsman
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Default RCV-91CD Tuning

I have read many of the posts here, but didn't find one similar to my problem. I have an RCV-91CD in a Hanger-9 Spitfire. The engine is mounted inverted. Using Cool Power 10% fuel, APC 14-6 prop. The engine does not start real easily, but requires about 5 seconds of cranking with an electric starter. It requires the throttle trim all the way up to start. Once started it requires the battery to stay on the glow-plug for about 20 seconds as it warms up. After it is warmed up, full throttle runs are good at 9200 RPM. After warm-up I remove the glow clip and the idle RPM drops 800 RPM. If I transition quickly from wide open throttle to idle the engine backfires or pops once, twice at most. For other 4-strokes this typically means the idel setting is to lean. I have richened the idle to 5 1/2 turns open. This setting gives a reasonabel transition from idle to high speed, but the acceleration is slower than the throttle movement, so it takes an extra second to reach top speed after the throttle is already at wide open. When I do throttle down from wide open with a smooth throttle movement, all is fine except the idle will stay high at around 2500 RPM and then slowly decrease to around 2000 RPM. The idle is reliable at 2000 RPM, below that and it will quit after about 15 seconds of idling. The engine has 1 1/2 gallons of fuel through it with 2 hours of running time. The signs that seem contradictory to me is the large drop in RPM when removing the glow clip, this makes me think the idle setting is rich, yet the bakfiring makes me think the idle is lean, am I reading the symptoms correctly? Do you have any ideas for a tuning procedure form here. The engine has performed well with only one incidence of quiting in the air which was after 1 gallon of fuel through the engine. I richened the high speed needle one click after that it has not quit yet. I'm guessing and hoping my problems are in tuning and not the engine..... Any ideas or help are appreciated. Thanks,

Scot