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engine operating temperature

Old 04-09-2007, 01:27 PM
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spiral_72
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Default engine operating temperature

Either it's not important or I'm searching for the wrong thing. I figured these forums would be the place to look.

I've got an HB .40 2 cycle engine (built in Germany) on an old plane I bought. It's about 10-15 years old. I'm trying to iron out my engine problems, so far with only marginal improvement. What kind of operating temperature should I expect??? At WOT it's running at about 245 F and at idle about 150 F. The thing is stalling on me and I'm trying to figure out why before I have to dead stick it in. Temp is a function of (not limited to) air/fuel right? If the engine is run lean it gets hotter leading to damage, right? I don't know if it matters, but the engine cools very, very fast after shutdown. I guess there's not much material there, huh?

It always starts and runs nice and strong with the glow starter. When I pull it off, the engine speed drops about 1500rpm, runs a little rough. It's much better now thanks to all my searches on these forums, but the problem is still there. It used to quit at 1/4 throttle with out the glow starter, run perfect with. Now it run ok (little rough) through full power without, perfect with. I've run through all the tests, tuning, pinch test etc, etc. It runs ok as is, just taxiing around the yard and then, BLAT! dead. No stumble, no stall, no nothing, dead.

I'm running 10% fuel. I put a piece of clear tubing about 3" on the exhaust pipe to direct off my plane. It doesn't seem to make any difference in the run. The engine is clean, with a 10x8 prop (I think). Although it's 10+ years old it seems in excellent condition. Hardly if ever run. New tank/lines/fuel. The exhaust has some fluid content to it, not a spray, just a spit occasionally, with a slight white smoke sometimes. No fuel filter and I'm positive the tank is setup properly, no foaming, with a 1/2 - full tank.
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Old 04-09-2007, 01:48 PM
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DMcQuinn
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Default RE: engine operating temperature

When you remove the glow igniter from the glow plug, the rpm of the engine should not change much at all. perhaps 100 rpm. this is true at high rpm and even at idle. So if yours drops 1500 rpm something is wrong. Could be a bad glow plug. these are relatively cheap and do wear out. Unlike a light bulb, they sometimes fail "partially". If the needle valve is set too rich this can also be a problem, but it sounds like you have been adjusting this a lot already. your temperatures seem reasonable. I'd get a new glow plug and try it (under $10).
Old 04-09-2007, 02:18 PM
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spiral_72
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Default RE: engine operating temperature

Maybe 1500rpm was a bit of a stretch. I'd say 500rpm easy. I'll try a new plug. I bought a few extra for just such an occasion.

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