With the piston and cam I needed more carb for RPM. I removed the choke butterfly shaft and assy. The bar is very thick and the round side can be bench ground down a lot. Watch the heat and your pressure so you don't bend your rod. Then take the choke butterfly and knife edge the front and rear on the bench grinder don't eat a lot of metal just sharpen the edges. Leave about three threads or 3/32" put it back together and use medium loctite on the screws. Then use a Dremel tool and grind the screws down about flush. Do the same to the throttle shaft screw in the front of the carb too. Make sure to clean all shavings out before reinstallation I used air and carb cleaner. I could feel more power all over. To retune mine I dropped the needle one clip #2 and raised the main jet one size to a 160. Just an idea until I spend the 500 dollars on a FCR. TC Racing sells bad *** Lectron carbs for $235...