My twin ran great untill I parked it in my shop. I got back on it 15min later, it cranked up fine and I drove it out back and I hit the throtle and the motor deided. It cranked back up fine but it would only idle. I drove it back to the shop and I did everything I could think to make it run right. I put a GOOD carb on it, re-torqued to head bolts,checked all the bolts on the intake,cheacked the flywheel key. But now it will only fire on one clyender. Is it the mag?