Classic/Antique Car Repair: miss fire, graham paige, miss fire

Question
I have an all original 1929 Graham Paige.  Car runs great but when you turn on the headlights and the motor is pulling hard, hills or high speed it will misfire.  If you turn the headlight off it will run and pull perfect.  Any ideas?

Thanks,
Scott

Answer
I would check the charging voltage with the lights on and the engine at road speed. If the voltage is low, below 6 volts, the generator system is suspect. This will limit the voltage available to the coil to fire the engine under load. If the voltage is ok then move the voltage to the + side of the coil. Repeat the test. If the voltage is low when the lights are on then there is resistance in the circuit between the battery and the coil, again lowering the voltage to the coil and causing the problem. Let me know the results and we will go from there.
Brad