My 87 has a horrid backfire when I let off the pedal to shift. I have reset the mixture screw, timed it, checked the vac lines and I still can't seem to figure out what might be causing it.

 

It also seems to be running super rich. Like passing raw fuel into the exhaust.

 

were you working on it lately? ie, plug wires, dizzy, timing? Tooth off on dizzy and/or crossed wires comes to mind. Any power loss? Backfiring through exhaust or carb?

 

mine used to backfire out the exhaust, would shoot a 4ft flame out of my turndown... bahahahaha. good way to scare some people

 

oh i didn't add any tech lol....mine was because my carb needed to be rebuilt and adjusted

 

I put a junkyard motor in it about a month ago. But it backfired before that. We did the timing right after. I had some vac lines reversed but they are all straight now. The plugs are relativley new along with the wires. It backfires thru the exhaust. Shoots flames like camo said his did. It also smells like its dumping raw gasoline out the turndown.

 

sounds like the aap diaphram is busted. pull the vac line off it and see if fuel dumps out of it. This might only affect the engine if it's cold but not warm As the vacuum to that is controlled by a bvsv.

only other thing I can think of is a sicking float.

same carb as the old motor right?

 

Yeah same carb. Ill try that and see whats up.

 

Now that you say sticky float. It does become flooded after driving it a while and I turn it off and let it sit. I tried the AAP, and no fuel dump.

 

I would lean towards float then. Might as well rebuild it.

 

Yep, for sure. I have a rebuild kit sittin in the shop. I will prolly tear into it tonite. Thanks for the help.

 

no problem, my advise does not come with a warranty though. Hope you get it all sorted out.

 

 

I replaced the carb on my 87 with the one off of our 85. The truck runs wayyy better but still backfires when I let off of the pedal at higher RPMs.

 

how are your mufflers and cat? also are u sure that the carb is not dumping gas in still after u let off the pedal? my 87 use to pop due to me putting an after market cap and muffler on that where high flow. not enough back pressure i guess or something..

 

They are both old. The muffler has a split from backfiring and im pretty sure the cat is the original, all in its 415XXX mile glory. Im sure that has something to do with it. The carb is not dumping fuel still after I let off of the gas. It ran 100% on the other truck.

 

Timing issues maybe?

 

No we threw a timing light on it today to check it. All was good.

 

0 degrees right?

 

He says no. Is that what its suppodabe? I not the best timing guy, I have my old man do it while I learn. Hes use to Ford though.