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Engine miss.

Old 05-22-2021, 07:35 PM
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Question Engine miss.

G'day all, this one has me scratching my head. OS sparky, while the 'plane is restrained it runs perfectly but as soon as you release it it starts to miss. Get it off the ground missing and farting, climbing out and it's fine but as soon as you turn down wind and take the load off the engine it misses and then goes deadstick. Checked the fuel supply which looks ok, changed the ignition system to no avail. Any thoughts would be muchly appreciated, I'm baffled and desperate.
Old 05-27-2021, 07:14 AM
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Assuming you have checked the tune and the engine is not too rich or lean....

How old is the fuel? In the US, they put ethanol in most of our gas, which means it only takes about 2 weeks to absorb water from the atmosphere and cause all kinds of problems.
I'd also suspect the spark plug. NGK seems to give less trouble than anything else in model engines, and also make sure it's gapped properly.
After that, a leaky reed valve (if it has one), air leaks pretty much anywhere, a bad diaphram or pump, or an inadequate ignition battery could all cause your problem.
Old 06-03-2021, 07:26 AM
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Sounds lean to me. As the engine unloads in the air it needs more fuel to turn the higher RPM. if it is lean or at peak on the ground it will run out of fuel as it unloads. The fact that it will die on a speed run downwind tells me that one way or another it is running out of fuel.

Old 06-03-2021, 07:42 PM
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This is very basic, but the tank lines could be the issue. A small tear in the clunk line where it joins the stopper can create a situation where the engine runs well in a normal G position but stalls under acceleration.

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