[Jim/GA]

Loud explosion backfire out of muffler/exhaust is caused by having a lot of unburned fuel collecting in the exhaust system.

This is usually because of faulty ignition. So the plugs are not firing (burning the fuel) and it goes into the exhaust.

So look at: bad condenser, ignition points in bad condition, point gap too small, bad connectors from distributor cap to plugs, fouled plugs.

An ignition switch going bad can do this, too. Or bad connections at the coil.

HTH.
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