I am not talking about the carburetor jets. I mean your electric choke known as the bystarter. Take out the two screws holding it in place and lift the choke out a bit when you are cranking the engine over.
it sounds like you have little compresion or you still have dirt that you arn't getting out. if the tank ain't cleen it will keep putting dirt in even a small bit will stop it.(because you said it will run for about 2mins which is plenty of time for dirt to interfear.)
fixed it, he had a intake leak, the carb was stripped and loose, a head leak ( i set him up with a high compression head) i cleaned the carb, more stuff came out. and he has about 70-90 psi compression. so i put a high compression head on, to even it out to run. got it going about 33-34. with new rings it will be soooo much nicer.
it seemed to bog out at full throttle. ok now I couldn't get it to 33-34 maybe because I'm 6'4" and 250 but it seemed to get good speed at half throttle. so what next?