If you have any smaller than a 14 on there, you should put on a bigger one, AT LEAST a 14. You want that torque at higher speeds too, ya know... Can you bore your carb? I made a 14 into a 16 on my Puch, intake too (this is a stock cylinder)... got much better acceleration at all speeds; in addition to +8 mph once geared up a bit. Leave the gears alone and burnout off the line, just adjust the clutch.
not sure what carb you have... but food for thought...