1971 Yamaha DT1 250 starting troubles

Just this week I rebuilt the motor of this exact model of bike. I bought it pretty cheap because someone had broken the piston rings. So I just put the rings in, and the bike fired right up. Next day, being yesterday, it wouldnt. I checked for spark but got small white sparks. So following clymers manual, started checking resistance. The book gives me resistance values for a m100-08 magneto, but my magneto is m100-16. Are the values going to be the same? Theres a red/white to black test which should have no resistance, but I am getting infinite resistance there. Is that my issue? Not sure how to proceed.

Thanks to anyone who can offer some advice