Low battery voltage. I'll bet you're running a 6 volt system, right? While you're cranking with the starter the voltage will be down around 4 1/2 to 4 3/4 volts, and the majority of the battery current is going to the starter. That leaves very little to power the coil. A roll start spins the crankshaft with the weight of the vehicle, and the ignition system is getting 5 1/2 or 6 volts to the coil. Hotter spark- - - -the gas lights off better.
Check the connections at the back of the ignition switch and the wiring to the coil- - - -I'll wager you're going to find some loose, dirty connections, or an ignition switch with bad internal contacts. A slightly dirty set of points will cause the same problem.
Jerry
