Originally Posted by ttpete
The exhaust probably has a catalytic converter in it, and maybe a restriction as well. The carburetor could have something in it that limits the throttle opening or there could be a restrictor between the carburetor and engine. I think you'll have to get some professional help here. See if there's an independently owned repair shop locally.
Do you think that might fix the stalling issue too? When I bought the bike the owner said that I have to leave the choke out at all times.