Bought a non-running '79 QT50. Replaced the charge coil and now it runs. I cannot seem to get it adjusted, even when switching between two Mikuni carbs. It seems to run well for a very short time, but then starts bogging off a dead start. Pilot jet is clean. Fuel/oil mix is clean. Once I get to about 15 mph it will take off and run really strong. It is pretty tough to start. Can someone point me in the right direction?