I'd betcha $100 to a hole in a doughnut, that it's you're carburetor solenoid. Or what ever that is on the bottom of the bowl. I had one that went bad, and did the same thing yours is doing..
A friend of mine said he was able to do something to an O-ring inside the bowl (where the solenoid) connects, and his runs fine now...
But, I'd stick with replacing that...