Heavy backfiring at low speeds

I don?t know if this should go under Cars & Minivan or Trucks so I?ll put it under both, as this is a small motor home.

I have family in New Orleans so was anxious to get there after Katrina and took off knowing that I had a deal hole on# 6 (burned valve). I?m driving a

1977 Concord motor home with a dodge 360-3 engine. I put in new plugs and a new carburetor before leaving.

It didn?t have all the power I would have liked but it ran OK and I made it there. I headed home (Tigard Oregon) after a couple of months and got as far as Phoenix Arizona. I don?t remember if there was a pop or loud noise of any sort but suddenly I could barely make 20 mph. I got towed into Phoenix where I was told that #1 and 3 cylinders were bypassing gas (raw gas squirting out of carb). He pulled the heads and we swapped for a rebuilt set. He seemed to do a good job and the engine ran fine. After leaving Phoenix I was able to make hills at 60 that would have been 45 before the heads were replaced.

I made about 800 miles and then everything went to hell. I could barely get it started and when I did, it sounded like it was a shooting gallery. It was backfiring worse than I?ve ever seen. This started about 20 miles from a city and I pushed on only to find that once I got above 45 or 50 mph it seemed to settle down and ran well enough that I decide to carry on because I really wanted to get home.

I finally made it and was glad to walk away from it. But now I need to get it fixed because I want to go back and work with Habitat for Humanity to help some of those people who have lost so much. But I don?t have a clue of where to start. I am thinking about shot gunning in a new distributor to see if that helps, but that is only a guess. I would really appreciate some guidance.

Reply to
Issy
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Sounds like excessively lean mixture which can cause the backfires you are seeing and also burn valves too. A burnt intake valve can cause bad backfiring too.

Reply to
TheSnoMan

It could be anything, but given your story and symptoms my guess would be the timing chain has jumped a tooth.

Newly rebuilt heads bolted onto a worn out bottom end is frequently a recipe for trouble. You didn't mention how many miles were on the engine before the first breakdown, but somehow I'd imagine on a '77 it was a lot. With the heads already off, how much extra would it have cost to hone the cylinders, re-ring it and put in new bearings, seals & timing gear & chain? Perhaps a new cam while we're in there. Probably double the original job but if you had done so, you would essentially have a brand new motor except for the carbeurator.

It is also possible the "rebuilt" heads weren't fully rebuilt. Some rebuilders will simply grind the valves & seats and put it back together with all the original hardware (valves, springs, lifters, push rods,rocker arms and keepers). I cannot imagine anyone putting newly rebuilt heads on and not replacing the springs and lifters, but I'm sure it happens.

Reply to
RamMan

Reply to
TheSnoMan

He also said thats gone with the rebuilt heads...

Reply to
CBHVAC

Reply to
TheSnoMan

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