In Reply to: Backfires posted by Cal Sexsmith on October 17, 2018 at 20:05:35:
It could be a fuel/carb issue, or, it could be an electrical issue. Did you do any tweaking to carb when you installed it? They are not pre-set out of the box. Many of us prefer to rebuild the original M/S TSX 241 carb, they are better than any new, aftermarket one sold today. You say it is switched over to 12 volts. Details needed. Do you have an alternator too? 1 wire or 3 wire? Is the Voltage Regulator in the circuit? Is he OEM Ballast Resistor wired correctly? Is the 6V coil used? If so, is there an in-line 1-OHM ceramic resistor in the circuit? Carb may need adjusting, or, wiring is wrong and/or shorted out. Sometimes an electrical short will cause misfiring/backfiring. Here's a document from our HOW-TO's forum/ELECTRICAL, on all the correct ways to wire these N's whether if 6V/POS GRN or 12V/NEG GRN. 99.98% of all non-starting/poorly running issues are due to incorrect wiring jobs, and the majority of those are due to some sort of 12V switchover job. Fouling plugs indicates it is getting fuel. When was the last time you did a tune-up?