Hi. Does that engine use a ballasted coil or non-ballasted? You could either be using the wrong coil or the ballast resistor has failed.
Is it a points system, or electronic ignition?
Defective cap, rotor, wires, spark plugs. Anything that will cause a plug to misfire or not fire at all.
Too high a voltage going to the coil, like 15 to 17 volts because the charging system has failed will also cause it.
