one thing you can try is to wrap the threads on your carb w/ teflon tape (you can get it at any hardware store). this will give you a bit better seal on the top of the carb, but you only want to do this long enough to diagnose if that's where your problem lies. you don't want to run it like that long enough for any bits to wear and migrate into your mixture and you want to make sure that you don't wrap the tape high enough to interfere w/ the action of the slide.
