Ditto on what has been said. Moving targets can drive you nuts. Most likley the fuel system but maybe not. Start with the basics first (fuel, comp., spark). Check the grounds for your ignition!!! It's an old bike and corrosion can be everywhere. Clean, tighten bolts, screws, put on lock washers to get a good bite into the frame. Might as well move on to a Comp. test or leakdown test before diving into the crank seals. If it turns out to be crank seals or ignition labor and parts may not be worth the fix. If you need new ignition parts, OEM can be SOL. A PVL or other after market ignitions can be upwards of $500!