The last time I ran into backfiring/afterfiring while under way at
around half throttle it was caused by leaky valves that allowed
combusting gases into the manifolds. This was on a '76 Dodge 360 V8.
The valves had receded into the heads and were no longer seating
properly. If your ignition timing is correct and the vacuum advance
works, a compression test may be in order.
Cheers,
CR
Douglas Gaither wrote:
> I am currently driving my father's '73B. It was not quite warming up so
> I installed a 195 degree thermostat. Everything was cozy. After about
> a week, I started experiencing backfires. It occurs after the engine is
> warmed up and under moderate throttle between 2500 and 3000 RPM.
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