Yep he’s still posting Wilber, so where you been hiding all this time??? This is a discussion forum, not Auto Repair 101, there aren't alway answers to the questions. I posted this to your PM this morning also!
The reason I never came back with a solution was that there never was a definitive solution so I saw no need to just blow hot air. After rebuilding and replacing about everything on the engine the last thing that I changed was the coil, even though the engine was running fine with the original coil. I never have been and am not now an advocate of off the shelf additives but about this same time I started adding Marvel Mystery Oil to every tank of gas. That was last year and I haven't had the backfiring occur since then.
I've always had a problem with the engine burning oil, because the oil scrapers are shot. It's not enough to see smoke out the tail pipe in the daylight but it is a significant amount and it does show up in a street light when you take of at night. By significant I mean a quart every 100-150 miles.
My only explanation for the back firing would be that the oil was forming deposits in the combustion chamber and every once in a while some would build up enough that it would cause a hot spot in the cylinder and pre-ignite the incoming mixture. This would blow out the bit of carbon until a little more built up. The MMO states that “when added to your fuel regularly, it keeps spark plugs and fuel injectors free of carbon deposits.” Now like I said, this stuff has always been snake oil in my opinion, but something is not happening that was before for a while on a regular basis. Then again, it might have just been the coil, but I have no explanation why this would cause this to happen when the engine was running normal other wise.
So, sorry I wasn’t of much help, nine times out of ten it’s a timing problem. About all I could possibly add to this thread is to make sure your timing i.e., valve and ignition are all set and operating properly, that you don’t have any burnt, bent or sticking valves, that the timing chain isn’t slack, that the distributor gear is not loose, no cracked cap or loose rotor, etc., then go from there.
Denny Graham
Sandwich, IL
