| i was finding that every 20 minutes i would either have fuel pissing out of my overflow, or the bike would die in the ass with anything more than half throttle.
both caused by dirt in the carb (on valve seat, of in jet respectively)
smashed open the fuel filter that came fitted on the bike. instantly explained everything. it was never put together correctly. it has a fine mesh in there, but the fuel was free to bypass it, along with any dirt in the fuel.
my 2 friends filters were the same, so i dont know if it is an isolated problem, or if there are hundreds like this.
$13 later for a new filter from a lawn mower shop, and i was away, never to be plagued with carb problems again.
if you do get one, make sure you let them know its for a gravity fed system, as ones intended for use with a fuel pump will be too restrictive.
hope thats of some help | 
