Hi guys, I have a basically standard 426 which ever since I went up one main jet size I have never been able to get it to idle sweetly. When warm it can just be sitting there running and suddenly the idle speed will rise for no reason, sometimes it drops back by itself and sometimes I have to give the throttle a blip to bring it back down. I also find it easier to start if I give the idle screw one full turn (up). Has anyone else come across this before? im stumped, I've cleaned the carb out many times.