need some carb help!!

[wolf263]

Hey guys..I just got a used 2003 blaster..the motor is stock..runs 50:1 premix..the guy I got it from was running no air box lid with stock filter and it had a 420 main jet..so I wanted to put it back to stock..put lid back on box and put a 230 main back in and it ran like crap so I jetted it the next five sizes and still crap..so I put the 420 back in and it runs good again..any ideas?

thanx

[~Smart-Parts~]

whats on the bike, If its completly stock then premix it to 32:1, becuase 50:1 is a little lean for stock motor