Not sure what you mean by on and off with the choke . If by off, you mean the air is restricted, and the bike will only run in this position, then I would say that the pilot jet or something to do with the idle system is your problem.If by closed, you men no air restriction, and it won´t run, then you have the same problem. Clogged idle system somewhere,... Without a doubt. 99% of all small engine ( Including motorcycle engines ) problems can be traced back to carburetion problems. Its a fact!.