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Phil..... ....lots of reasons engines "back-fire". Could be bad ignition timing. Could be leaking intake manifold. Could be leaking exhaust somewhere. Could be incorrectly adjusted carburator. Could be bad sparkies. Could be alotta things. Maybe sticky intake valvestems. The only way to test that theory is the dreaded compression test. Take all your sparkies outta the cylinderhead so it'll crank eazier and faster. Crank for 5 puffs min and writter down. Then add about 1 oz, tablespoon, or 1-squirt of engine oil and take yer wet compression reading again and ritter down. Evaluating yer readings, Ford specs: 90 psi min (dry) If'n wet compression is greater than 20 psi over the dry compression, you've got worn piston rings. If'n NO CHANGE, wet vs dry, you've gott bad valves, most likely burned exhaust valve. If'n yer dry compression is about 70 psi, most likely sticky intake valvestem. If'n ya gotts 2 adjacent cylinders with low compression, most likely blown headgasket. But what do I know, I flunked mindreading, just ask my ex-wife..... ....Dell
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