I was riding wit some buddys and my 300ex just keeps shutting off in trails and I thought it was the wire that kept coming unplugged by the rear brake lever where my foot is but no that solved my problem of tackin out early but not it just keeps shutting off every 30 seconds to a minute in a half so what do u think it is[/QUOTE
Check the two simplest things 1st......
1) make sure tank is breathing ok at fuel cap
2) make sure you have good flow at petcock and even if you do still check bowl for debri
3) drain the bowl (simple gold screw on side of carb I think) in container inspecting for debri in gas (spec of dirt may be surfacing to main jet constantly?)
It could be electrical too and would check for spark immeadiatly after it shuts off.