1972 20hp Mercury Thunderbolt ignition (pull start) engine is firing only on the top cylinder. I've swapped the coil wires to check for a bad coil and that's not the problem. Both coils are good. Spark plugs and wires are good also. I tried pulling the flywheel and trace the bad wire(green)down. I can see where it goes in, but can't get the flywheel off to see where it connects to. Where is the power pack on the engine, or does it not have one? What could be causing the engine to fire on 1 cylinder only? Both spark plug wires are producing spark, even the one that doesn't fire the bottom cylinder. IT shocked me when I had the motor running.
