What do you mean it doesn't start?:confused2: Does it turn over or does it do nothing when you turn the key? If it doesn't turn over it could be a safety switch or maybe a blown fuse since your hooked up the charger backwards. If it turns over but doesn't start, it could be you are not getting fuel to carb or you have a fouled plug. Also could be a safety switch that shorting out coil. Are you getting spark at the plug? May need to give us a little more info so we can help you.