Motor runs fine but stalls at high rpm

[bcbristoll]

I'm having trouble witlh my idle speed. The engine starts easily and runs fine...that is until I Throttle down. When I do, the engine just stalls at pretty high rpm. there is no studder...no nothing it just stalls. Any ideas ?? I'm planning on pulling the carb in the spring and rebuilding but just can't understand why it just cuts out.

[Administrator]

Electric fuel pump?

Bill

[edwardc]

I can think of two possibilities:

1. Clogged or dirty Idle Jet
2. Stuck centrifugal advance weights

[joe_db]

I am voting for clogged idle jet myself, but it is always worth checking the fuel pressure IMHO. Not sure about stuck weights, if stuck retarded the idle would be fine and I think stuck advanced would cause rough idle, not sudden cutoff. Very easy to check though.

[Dave Neptune]

I'll go with a plugged jet or a vacuum leak. Check for the leak before removing the carb.

Common vac leaks are the scavenge tube, the carb base and manifold carb base gasket(s) if equipped with a PCV valve which can be easily plugged for checking.

Dave Neptune

[capnward]

I had that problem, and it was a piece of crud in the idle jet. I removed the jet and held it up to the light. I could see the obstruction. Cleaned it out with a thin wire from a wire brush. Now I remove and clean the carb and inspect the idle jet every spring. That procedure should be something we A4 owners are comfortable with.

[JOHN COOKSON]

Lots of good ideas have been posted.

Have you tried simply adjusting the idle mixture? Or maybe the idle speed adjustment has slipped.

Turn the idle mixture adjustment screw in till it seats then back it out 1 1/2 turns. If this gives you any an idle you can further adjust from this setting.
If you can't get satisfactory idle by adjusting the mixture and or idle RPM adjustment you will need to clean the carb or look further for the problem.

TRUE GRIT

[ndutton]

Timing

In addition to the excellent carburetion/mixture suggestions, proper timing makes a huge improvement on idle behavior.

[ED.D]

I will 2nd idle jet adjustment easy to try and it has fixed the same issue with me a number of times