Check the Plugs, wires, then coil. Mine was running like that last year. Buy a Polaris replacement coil too. Bought a cheap one and it lasted 1 week. Put the polaris in, 600 trouble free miles.
A couple more ideas to go with the other suggestions. Unplug the single black/white wire located between the oil tank and the air box and then see if you always have spark. That would eleminate the engine stop circuits keeping you from having spark if you were to have a bad kill switch. switch in the throttle block, or ignition switch. Also look for bare or rubbed wires right where the wires go into the starter housing.
