I had a friend rebuild my Street Averager 670cfm. We put it on the 360 and filled the float bowls through the vents. It fired right up with no issues. We shut it down and fired it up several times. Worked great! It sat overnight and would not start. I poured gas in and got it fired up that way. Once it ran for a min or two, it would shut down and start right back up with no problems. Fuel pump, timing, and float levels are good. I am stumped. What would cause this problem?