I just read the aggravating 426 thread and I didn't want to throw mine in with his and steal his attention...so heres mine I have posted on here about my bike doing almost the same thing. I re-shimmed all valves and re-checked...they are good...I put a new plug in it. I have pulled the carbs multiple times and cleaned them, they look pretty good, and the bowl is full. Today I adjusted the throttle stop screw waaay up and it started firing almost every kick, but not staying running, and then yeah eventually too much and it wouldn't fire. I am wondering if maybe the vacuum you speak of could be bad...Now is this from tightening the clamps around the boots tight? I am not too tight, but I thought tight enough. Also when I rode this bike before I could run it allll day and never once have to start it with the hot start pulled....How does this work and could that be a problem? Thanks again.