When I would attempt a cold start and fail the first try, when it would start on the second attempt there would be a sharp or crisp sounding clacking for a few seconds and then it would abruptly stop. I am guessing the compression release is confused?
It has not done this since I backed my pilot screws out because it starts on the first try. But I am still curiuose.

 

Your guess is correct! It is the compression release counterweights slapping at low idle speeds. You might want to increase the idle speed a bit.

 

Thanks.