Thanks all for the replies and advice. A couple if the things you guys have mentioned I had already tried and neglected to mention.
I have had the rocker arm cover off while the engine was idling and all valves and push rods seem to be about normal (Nothing not moving or bent). I have brought #1 up on the compression stroke (about 180 degrees of crank rotation after both valves have closed and their push rods spin freely). At this point the flywheel dot lines up with the pointer and the distributor rotor lines up with #1 spark terminal. Also sure I have the firing order correct 15 to young, 36 to old, 24 just right (I was younger when I memorized it). I have had it running for about an hour while dinking around with the distributor trying to make the problem go away and have seen no evidence if a head gasket leak or of a cracked head. (No bubbles in the rad no coolant leaks and no discoloration in the oil)
The odd thing is that the engine starts and idles fine (I don’t think it would even run with the timing off 180, or even one tooth). The backfiring is NOT at a set frequency.
I’m beginning to like the suggestion to check the condenser. And ordered all new ignition stuff this AM (cap, wires, rotor, points & condenser) I’ll post the results here or be back for more advice.
Thanks again
