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Rich or Lean???

Old 08-08-2007, 07:34 AM
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reincarnate
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Default Rich or Lean???

First off, the engine is a new Evolution 26GT2, with a fully charged 2c lipo on ignition. I have run the engine in according to Pe and others advice at 30:1 for 1 gallon on the ground so far. I'm getting about 8300 RPM with a bisson muffler (engine is side mounted). Transition is great on the ground, and have had no problems thus far. Last weekend I finally got the airplane to the field, started and warmed up with no problems...RPM stable, transition smooth, good idle. When I took to the air (maiden for airplane and engine) and made got her flying, I noticed that the engine would "bog", for lack of a better term, at full throttle. 5/8 to 3/4 throttle seemed fine, but when advanced I would loose RPM. Transition was still good up to that point, and it didn't die, but never got a full throttle response. Flight time was less than 5 minutes due to this, and haven't had another chance to get it in the air since.

How do I figure out whether I went lean in the air, or if I was too rich? It ran good on the ground after, so I'm a little unsure of which way to go. I realize that this is a very open ended question, so I'm just looking for possibilities.

Weather that day was hot...nearly 90 deg F and roughly 95% humidity, with a storm on the horizon. Engine didn't feel hotter than normal (forgot my infrared temp gun) and I don't believe I was hot, due to short run time. The plug coloration is just a hair darker than perfect. And I am still running a 30:1 mix (Yamalube synthetic racing blend) w/92 octane (US) gas.
Old 08-08-2007, 08:53 AM
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BaldEagel
 
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Default RE: Rich or Lean???

Sounds to me as though it went lean in the air, on the Walboro carbs the low end neddle has an effect at the top end as well as the low end, I would try richening the bottom end first and see what happens in the air as it runs OK on the ground at the top end.

Mike
Old 08-08-2007, 08:51 PM
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reincarnate
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Default RE: Rich or Lean???

Something I failed to do was mention that there seemed to be a carbon build-up on the bottom of the threads of the plug. Tonight I pulled the head off of the jug and there is a large black spot on top of the piston that simply looks like burned oil. Indicator of something or normal? The walls of the cylinder look great, it's just the top of the piston. As a note, it's the plug recommended for the engine. Put in a new plug tonight (same type) and ran it again, (first time since flight Sunday) and now I'm getting close to 9300 RPM with no lag in top end like I had in the air. Richened the low end a bit and noticed no lag in throttle or high end. How do you diagnose a problem you can't replicate?

BTW, engine temps tonight, running on the ground with a 94 deg ambient (sheesh!!) were 272 deg F cowl off, and 260 F cowl on. The baffles are working Pe! Thanks for that.

Old 08-09-2007, 06:34 AM
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Default RE: Rich or Lean???

When an engine seems to bog down in flight, and not on the ground, it often is a rich condition. First thing to check is the plug. In these cases on board temperature monitoring is very valuable and will show a lean or rich condition by respective high or low max temps. Failing that, only plug readings will help you get tuned well.
I am glad the cooling system works well. The 260F range is fine. Sustained restrained ground running is a most severe condition for the engine. In flight conditions will be better.

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