old truck backfires

Anonymous-0 · Oct 23, 2010

Looking for help to stop backfiring. Got a 70 391 ford that I have put new plugs, plug wires,points,condenssor. Carb cleaner and blown carb out with air and timing check. Still backfires . Waht could be causing this. Thanks for the responses.

LOU from WI · Oct 23, 2010

Check the timing,make sure it didn"t jump time.Also check fuel flow,and is the choke closed?Is the point gap set right?Is there a sticking valve? or bad compression?If any of the above is fine check the wiring for the points,coil,condensor, make sure there are no shorts in the wiring.All the grounds good on the truck ignition system?About all I can think of as of now.Hope it helps.
LOU

bob15 · Oct 23, 2010

Was it backfiring before the tune-up? Is it backfiring threw the exhaust or up the carb?

bob

rustred · Oct 23, 2010

you need a camshaft and lifters. none of the things you replaced will cause a backfire.

Mathias NY · Oct 23, 2010

I'm no expert on the old Fords, but I had a Chevy with a bad vacuum advance line on the distributor that had the same issue. I changed the line and the problem went away.

If consider a stuck valve too. A compression test should rule that out.

Good luck.

old · Oct 23, 2010

Many things can cause one to back fire. If it is running lean it will back fire. If the timing is off it can cause it to back fire. Valves sticking or burned or set wrong will also cause that and even the points being set wrong can cause that

Anonymous-0 · Oct 23, 2010

yea it bakfired brfore tuneup and it backfires out the exhaust not carb

Too Far Gone · Oct 23, 2010

My cousin fought this for a long time.We finally fixed it right up with a rotor and cap on his truck

Keith-OR · Oct 23, 2010

Need to know if it back firing back though the carb or out the exhaust.
You need to see if 7 & 8 spark plug wires are leaking. These 2 wires run Side by side they can induce voltage into each other since the firing order is 1-5-4-2-6-3-"7"-"8".
Start engine up after dark and check to see if you have spark running on the outside of wire insulation.
Carbon build up on top of piston can also cause back firing.HTH

You have enough info from all that has posted to keep you busy for awhile..

Good Luck

Keith & Shawn(Gold Medal Winner)

teddy52food · Oct 23, 2010

Check the firing order. Ford numbers their cylinders different than most others. 1-2-3-4 on one side & 5-6-7-8 on the other.

JDseller · Oct 23, 2010

A exhaust leak in front of the muffler can cause a exhaust backfire when the engine is hot. I would check the manifold and work my way back. I had a Ford Galaxy 500 that would break the manifold donuts. Would sound like a shot gun when you let off of the gas pedal. The exhaust gas is still hot until after the muffler. You add in fresh oxygen rich air and you have a back fire. Check manifold gaskets, donuts, and exhuast pipe.

Owen Aaland · Oct 23, 2010

Under what conditions does it backfire? All the time? Idle only? Higher speeds only? Only when releasing the throttle after running at higher speeds?

That information can help determine the cause.

rustred · Oct 23, 2010

well since its out exhuast when does it backfire, when you let off the gas driving. be nice to get complete info. before one starts diagnosis. thats one problem here , so often not enough info then everyone is pulling ideas out of the sky.

Brian Jasper co. Ia · Oct 23, 2010

I'm guessing it backfires on deceleration. Does it have one of those smog air pumps? If it does, and the divert valve isn't diverting the air away from the exhaust on decel, they backfire quite a bit. Another thing to prevent backfires was a device called a "Dashpot". The dashpot slows the last bit of throttle closure to prevent backfiring and stalling.

old truck backfires

Anonymous-0

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LOU from WI

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bob15

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rustred

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Mathias NY

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old

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Anonymous-0

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Too Far Gone

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Brian Jasper co. Ia

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