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B-85f Backfire....

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:pat: I HAVE A 1956 MACK B-85F FIRETRUCK THAT BACKFIRES BAD. IT LOOKS LIKE THE PREVIOUS OWNER BLEW THE MUFFLER APART. I HAVE HEARD SEVERAL SUGGESTIONS ON POSSIBLE CAUSES-ANY IDEAS?

THANKS..

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I am having the same problem with my 1948 mack l-model with a enf707a gas engine.

I'm working on it now. Have you come up with any ideas yet? If I find the problem with mine, I'll

let you know.

:pat: I HAVE A 1956 MACK B-85F FIRETRUCK THAT BACKFIRES BAD. IT LOOKS LIKE THE PREVIOUS OWNER BLEW THE MUFFLER APART. I HAVE HEARD SEVERAL SUGGESTIONS ON POSSIBLE CAUSES-ANY IDEAS?

THANKS..

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Check for a blown gasket where the exhaust pipe attaches to the manifold, or any other loose connections in the exhaust system upstream from the muffler.

I remember a long time ago I had a Ford F 750 with a big gas engine in it, and it would backfire something awful on deceleration.

Noticed that it had a broken stud where the crossover pipe connected to the left exhaust manifold, which allowed the pipe to come loose.

Fixed the stud and got that pipe to manifold connection tightened back up, and the backfiring went away.

I've heard others talk of this happening too, caused by a loose connection in the exhaust system.

Evidently on deceleration, air is pulled into the exhaust system thru the loose connection, and mixes with unburned fuel in the exhaust system, and then is ignited by the heat in the muffler, then you get a big "bang".

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A bad condenser will also make a gas engine backfire like mad. Give that a try, Art :thumb:

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Thanks for the advice, but I think it may be more than that. Right now it dosen't run. It cranks great, but dosen't even try to start. After about 7-10 seconds of cranking, it explodes out the muffler. All of the ignition parts are new on both systems: plugs, cap, rotors, ext. Carb has been rebuit. Adjusted the valves. Even the timing "looks good". It also has good compression. I think I will try disconnecting the muffler. It may be clogged up from the last owner running the truck for miles with the choke on when the throttle got stuck. The only ignition parts not replaced are the coils. Will test them next.

Also in need of a manual for the ENF707A if anyone haas one for sale.

THANKS

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