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Mar 24, 2002 | 10:29 PM

Martin85xl

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Joined: Feb 2002

Posts: 28

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From: Poland USA

Backfire

I could use some help. I have an 85 F250 with a 351w, 4brl.carb auto trans, about 70000 mi. I get some pretty severe backfiring, mostly in the morning when it's cold. I'm afraid my neighbors are circulating a petition.

Mar 25, 2002 | 09:13 AM

tomw

Logistics Pro

Joined: Jan 2002

Posts: 4,907

Likes: 39

From: suburban atlanta

Backfire

If it is backfiring thru the carb, probably choke is too lean.
If it is backfiring out the exhaust, probably have something wrong
with the AIR pump or control valves. Check for loose, broken, or
cracked vacuum lines under the hood. Some engines have a 'gulp'
valve that stops air pump air flow when you slow down so that the richer mixture on cold start cannot explode in the muffler/exhaust.
UNEEDA book to know what your system has...
I'd also check the plug wires for a possible cross-fire. Plug wires
should cross at a sharp angle to prevent firing a plug inappropriately.
Once the compose reply window opens, the original ? is not visible,
so I can't remember the engine/year, etc.
Some places to look...
tom

Mar 25, 2002 | 10:17 AM

Mil1ion

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Backfire

Engine timing
Cracked Distributor cap,carbon tracking, or condensation in it

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Mar 25, 2002 | 09:26 PM

rocky2

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Joined: Apr 2001

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Backfire

Backfire though carb=dist.cap/wires/

Backfire in exshaust=pollution air pump diverter valve.Take off belt and check

Mar 26, 2002 | 08:46 PM

Martin85xl

Thread Starter

Freshman User

Joined: Feb 2002

Posts: 28

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From: Poland USA

Backfire

Thanks for the help. The backfire is through the exhaust. It runs real well once its warm and even when its cold except for deceleration and sometimes starting, if it does'nt start on the first crank. Someone mentioned a dashpot on the carb that may be bad or need set.

Mar 26, 2002 | 08:51 PM

Martin85xl

Thread Starter

Freshman User

Joined: Feb 2002

Posts: 28

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From: Poland USA

Backfire

I've been chasing a squeeling belt. Could this be the air pump? Can I get rid of the pump? I would like to install headers in the future and that would simplify things alot. Again thanks for the help

Mar 27, 2002 | 12:41 AM

skyranger_ca

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Joined: Mar 2001

Posts: 6

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Backfire

I have the same truck with dual air pumps.Had same problem,Have two air diverter valves on the truck, one feeding both exhaust manifolds and the other feeding to the rear pipe connecting the heads.The front valve was was not working.I took the rear valve and swapped it for the front one and put the faulty front one on the rear. it cured the problem. I ran like this for a year and finally got rid of the air pumps. hope this helps