I overhauled my buddy's Jubilee about 6 years ago. Put all new plugs, wires,condensor in at that point and ran fine until about 1 year ago. Replaced points, condenser, coil, plugs, etc again. Starts up cold, runs, let it warm up some, work it and spark starts fading watching a spark tester inline. Engine starts to miss and sputter and shuts off. Tractor is all original with 6 volt positive ground and generator. I checked polarity of coil with battery negative being fed from the switch and positive side going to the points. The generator charges, battery voltage is staying up to about 7 volts. I even put power directly to the coil, and made good engine ground back to the battery and still does the same thing. What's next to do? 12 volt conversion with pertronix electronic ignition? Any input welcome and thanks in advance!