Well, I tried out this thumbscrew style air/fuel mixture screw from factory pro. I can't seem to get rid of my low end throttle stumbling. Mid range and full throttle seem fine and the bike pulls hard after I get moving. But from a stand still, it burps and sputters like crazy. I've tried 3 different pilot jets with no change. I tried the stock 55, a 58 and finally a 65. Nothing seems to help. I'm wondering if anyone else has tried this type of A/F screw and if they had any problems with it. The problem goes away when I choke it a bit and I definitely don't have any vacuum leaks. My X is running with a Hypercharger and HK slip on pipes. I'll probably pull the carb down tomorrow and re-install the original A/F mixture screw and see what happens.