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os 91 fs tends to die after 20-30sec idling

Old 11-10-2006, 02:28 PM
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rxAxilleas
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Default os 91 fs tends to die after 20-30sec idling

I have an os91fs that works fine at high end but if i set to idle for about 20-30 seconds seems that many fuell comes to the engine and tends to sease fire or the type f plug goes cold. so i must give a litle revs every few seconds to clear the engine from fuell or to warm the plug. i tried to lean the mixture (low end)but nothing hapens.it seems that its a plug problem.i know that type f is the hotest plugs . what can i do?my prop is master air screw 14/7 and revs at 8500 .the idle is set to 2700-3000. when i conect the glow starter i have very stable idle for as log as i want at about 2500. also consider that the engine is inverted on a h9 p47.is something wrong with my engine? can i use smaller prop? with that idle it is imposible to keep the plane without moving.i thing a 13/8 prop.
thanks
Achilles
Old 11-12-2006, 12:12 PM
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ChrisMH
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Default RE: os 91 fs tends to die after 20-30sec idling

Mine did exactly the same thing. I had to lean out the low speed needle quite a bit (1.5-2 full turns, if I recall) to get it to idle reliably. Make sure you don't lean it too much, though, or the engine will die when you transition from idle.

I don't have a bunch of experience here, but from what I've read, you lean the low speed needle until the engine acts like it's going to die when transitioning to full throttle. Then richen it until it transitions smoothly. Worked for me, anyway.

I'm still breaking the engine in, but my idle is around 2600-2800 with a 14x8 for as long as I want.

Chris

Old 11-13-2006, 12:50 PM
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Bax
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Default RE: os 91 fs tends to die after 20-30sec idling

You may have to lean your idle mixture. The easiest way to get the engine set up is to have it upright on a test stand. Then the settings will be very close to what you'll need for inverted running. Also, make sure the fuel tank's not too high. That can also lead to problematic running.

Inverted engines tend to be more problematic than side or upright engines. That's because the glow plug can act as a sump at low throttle settings and get flooded out by fuel. An on-board glow plug battery that comes on at 1/3-1/4 throttle usually cures the difficulty.

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