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I noticed some fire coming out of my tailpipe this evening. I was coming down a long steep hill, engine braking the whole way. About 5 minutes in I noticed some orange light in my mirror. It was fire coming out of my tailpipe. If I cracked the throttle just a little it went out. The truck runs fine. I have never seen this before and wondering if anybody else has. I am guessing one cylinder is not firing in that condition.

Mine does it all the time. The bangs a are quite loud too. The problem is that air is coming in somewhere near the exhaust manifold and unburnt gas from the idle jets/idle screws re-ignites down the exhaust.
I have not been able to lean it enough to avoid it, but if I fix all holes in the exhaust system, it goes away. My problem is in the flexible union between manifold and heater.
Lately, I just turn the ignition off on long downhill runs. The idle valves close and all the backfiring stops.

I have always wondered if it was possible to rig up something to shut the idle valves during engine braking. I thought doing so might help with the stench. I will look for some exhaust leaks

The idle screws make a small difference, but I run into a dead power zone between 1000 and 1500 rpm. I believe this is due to small vacuum leaks. The last one I found was from the gaskets of the choke plates.
Smoking the manifold and carbs to look for leaks is very important.

I've been having some backfire issues lately as well. I bring this up in reference to what boeing7873 mentioned as I too have some leakage where the exhaust header pipe mates up to the flexible union. I am kinda suspecting this may be contributing to my issue.

I'm probably going to disassemble the SAV supplied clamps at this spot and see if there is any way I can improve the connection at that point.

Anybody have any suggestions as to a better clamp at this spot?

The ideal solution is a true flexible connection between the manifold and the heater intake. SAV sells a kit, quite expensive, but looks good. I have not tried it as I find it quite expensive. I welded two short flexible connections bought at the local store and I believe they are too rigid. No clamp will solve the problem. Flexibility is the key.

Change clamps to t-bolt full radius type. I find that these work best. Never weld any couplings to header pipes. It complicates future repairs.

Thx for the tip on the T-Bolts Jim. And as a bonus they are stainless steel...............winner

Jim LaGuardia wrote: ↑Mon Aug 09, 2021 11:57 am Change clamps to t-bolt full radius type. I find that these work best. Never weld any couplings to header pipes. It complicates future repairs.

Totally agree with Jim. When I meant welding, I was referring to the flexible adaptors to the plates bolted to the heater side. And good clamps are a must but only after you figure out the flexible segments. Something needs to move or something will break.