I have a Victa flat twin mower (170ccs) with a twin spark magneto coil, which I can only get to run if I disconnect the front cylinder spark plug lead, connect another plug to that lead and earth that plug. It will then start and run well but on the other cylinder only while the other plug sparks furiously on the base plate of the mower. If I rev it up very high and quickly Flik that plug out and re-connect the lead to the original other plug , it will continue to run, but If I miss the quick change over, re-connecting the lead causes it to stop. What is happening here? I hope someone can tell me.