Do you have both the carb and petcock vacuum connections blocked off?...
If you do... then your petcock is fine... 'till you get a Raptor...
It may just be condensation in the pipe,.. (white smoke is usually water vapor)... (the exhaust heat will evaporate it)...
Blue/gray is oil... black is fuel...
Adjusting the fuel mix will do nothing... unspent fuel would be very black smoke...
...
Some fuel additives, like Sea Foam will cause white smoke, too...