i had he same problem with one i have,i did two things first loosen the carburetor op hold it down with your thumb and retightn it,my oring wasn't sealing all the way,also check the low end to make sure it is set properly,the air bubbles that JIM C was referring to,is that you might have a leak in your inlet fuel line from the fuel tank,maybe the clunk or fuel line itself.hope this helps