UL912 Intermiddent engine failure

I would say that it is highly unlikely that it is an ignition problem if the engine stops completely. The ignition circuit have no common components electrically speaking. You would have to have to have a simultaneous failure in both generator coil circuits or both ignition kill switch circuits. I seem to recall that on some of the very early engines the generator coils shared a common ground behind the flywheel. I might be wrong.

I would suspect a fuel problem. This is what I would be thinking:
Do you have a fuel pressure gauge?
What is the pressure like during the rough running?
Are the floats OK?
Is there any debris in the float bowls?
Is the fuel filter clean?

Hi Kevin

It's not "rough running" as you write, the engine is like "on-off-on" for a split second, that's why the ignition is suspected.

1. Fuel pressure gauge stable, no fluctuations during engine intermittent "on-off-on"

2. Floats weight and float height according to the AMM.

3. No debries or water in float bowls.

4. Fuel filter clean.

5. New fuel hoses installed firewall forward.

If you are convinced that it is ignition then take a look at the generator coils and the trigger coils on the back of the engine. Could you have a faulty ignition key switch? Are the high voltage coils grounded at the same point and is it corroded?

It might seem like an obvious question, but are you certain that both ingnition circuits are operating properly after start up?  If one has not been working, it might not become obvious till the other one actually starts to act up.

Hi Tyler

Mag drop is a part of the check list, both ignition systems operates normal individually.