Hy Powerwagontim, when you converted it to 12 volt, what type of coil did you use? There are coils that are made to use 12 volts all the time, and others which must have a ballast resistor installed in the circuit before the coils primary connection. If you use a coil which requires a resistor, without a resistor, the coil will overheat and break down, the engine may idle fine, but will misfire more and more if you can get it to rev up. Check what type of coil you have, and either replace it with one that can be fed 12 volts all the time, or install a ballast resistor in the coils primary circuit. The only other thing that I can think of that may cause the problem you have is a bad condenser, good luck.