Compression is very good, there are no leaks on the crankcase (I made sure every bolt was tight before monting it in the test stand), as I type this, only thing different other than enlarging the venturi size, was that I soldered shut the little hole in the butterfly, maybe this had something to do with it, but I doubt it, I will take it apart again and see if there is something suspicious in the diaphragm. I will let you guys know is I find something, go figure this one! By the way, the noise is not heard if there is no fuel in the carburator.