I have purchased 3 brand new OEM old style carbs simply because these carb issues drove me nuts. It is a royal PITA pulling the carb off and putting it back on so many times. When the new carb arrives I yank the plug over the pilot screw and set it at 2 full revolutions out from bottom. Once the bike is running and hot I can then set the final fine tune. All three new carbs performed perfect right out of the box. I went so far as to have the old and new carbs side by side as I opened them both to compare and be sure I did not have some part wrong in the old one. Sure enough I had a tiny spring in the wrong place and my float was not set right. Fixed that and the carb worked perfect. Shims and different jets might be fine if you are riding in high altitude or looking for every last drop of power but they must be done in a known working carb that is running the bike fine to begin with.