Check your low end needle, it sounds like you got the low end lean and the top fat. The low end is what you're mostly on while in the infield going from corner to corner and you only go onto the top-end needle for brief moments at wide open. That is why you still see plenty of smoke, but it won't cool down. Try the pinch test on the fuel line just before the carb and if it revs instantly or dies it's too lean, you should get a count of 3 or 4 one thousanths before the idle rises ( do this after engine is warmed and do a good full throttle run and bring it in and do this quickly ). Hope this helps!