Cyberian and Frankman: It does run smooth at 12MPH. Once it gets up to 12MPH, its almost like it has a governor on it that holds back more speed!
The next two things I will check are fuel flow and air flow. Have a new air filter on order, due in next week. I may even try removing air filter and running it to see what happens.
Also plan on replacing leaky petcock. I will try to fit a 1978 NC50 petcock on the '79 PA50. I hope they are compatible.
Good advice so far and very much appreciated!