Occasional Miss at Idle

[marthur]

Last season our A-4 showed a symptom that puzzled me.

When motoring at idle it would occasionally miss. It sounded just like a cylinder would not fire, but only once in a while.

At higher revs we noticed nothing unusual. It also started well and otherwise gave no trouble.

I wondered if I had leaned out the carb too far, or if we need to check an ignition component. Someone told me they had the same symptom as their coil was just beginning to fail. Any thoughts or suggestions?

Mike

[Don Moyer]

Mike,

The fact that the engine runs OK at RPM above idle does sound like some tiny particulate may be trying to work its way through the idle system. Enriching the idle mixture slightly may help a bit, but if the problem continues you may have to disassemble the carburetor and clean out the idle passages.

Don

[marthur]

Thanks Don,

Your suggestion is a good one.

Now, compulsive that I am, I am wondering where the small bits came from.
Last season we rebuilt the fuel pump and found numerous small cracks in the diaphram. I wonder if small bits of rubber came off the diaphram and contributed to the idle issue? Or perhaps a bit of dust from a fiberglass job we did...

We'll probably never know, but this is a great time to do carberator work in Michigan!

ma