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erratic idle PAP ROS 125


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Carburator: Walbro 24

After warming / running up for a few minutes, the idle varies between 2100 and 2400, continiusly increasing and decreasing slowly.

I had the engine in for service with the distributor, but the idle is still like this and has been since I received the engine brand new.

Any ideas? I don't think it's the fuel system as I've replaced all tubes and the 2 filters. The colour of the spark plug is okay (light brown).

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Sounds like possible air leak.

Either carb side or maybe even from exhaust manifold?

It the timing fixed or adjustable? Possibly backplate moving, changing timing with vibration.

Could be an air leak from the carb side or exhaust manifold, but I doubt it since it has received full service recently. Maybe gasket or something in the carburator?

The ignition timing is adjustable with the ignition wheel (which also is a fan) on the back side. But changing the timing requires losening the ignition wheel which cannot be done while the motor is running...

I have a "catch" filter below the tank in order to avoid the motor stopping at low fuel levels (torque while airborne can move fuel away from the fuel exit on the tank), in addition to a smaller filter further up just before the fuel intake on the carburator. Frequently I can see "trapped" air bubbles in this 2nd filter. The bubbles appear to be trapped on one side since the filter is not aligned perfectly vertical..

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