backfiring problem

[plum_cuda]

I have a 1972 Barracuda with a 383 in it. The car ran great until about a month ago when I blew out the power valve in the holley 750. So i had the carb rebuilt and put it back together. I couldnt get the car running good at all and was barely able to get it out without horrible backfiring. So i took off that carb thinking that maybe something happened when the guy rebuilt it and I put on a holley 650 off another car that I have. Now I have gotten the car somewhat drivable but it still backfires alot and does not run how it should. I cant seem to find any solution to this problem. I have tried adjusting the idle mixture screws every which way and even though the backfiring decreases a little i cant get rid of tyhem and cant get it to make it run better. Hopefully someone who knows a bit more about tuning can help me. Thanks

[mtrv8n]

sounds more like a timing problem..

[mr.b]

is it backfiring through the carb or the exhaust?

[plum_cuda]

it is backfiring through both the carb and the exhaust but mostly through the exhaust

[1972roadrunner]

intake leak?? maybe your timing is too far advanced...is there any pinging?? does your dist. have a vacuum advance? maybe the canister got stuck...

just some things to think about...frankly i'm not too sure. kinda sounds like my brothers car... we advanced the timing though because the vacuum advance doesn't advance...its sluggish at lower rpm, but up around 4000 - 5000 rpm it runs great! his engine is a 440.

[timty2]

plum_cuda,

Did you make any recent changes about the time this started to happen? What type of IGN are you running? The blown power valve sounds like a symptom and not the cause.

A quick story: A long time ago, I upgraded to a MP ign and used MP (Taylor) spk plug wires. I didn't realize that the wires I ordered were a metal/non-suppression type core, and with the way I routed the wires, it interfeared with the magnetic signals used by the ECM. While I did not have the backfiring problem you describe, I did have a rough-running, high speed missing, overheating monster 440!

Just keep in mind... even a simple spark plug wire change can lead to apparent "Unrelated" problems like this. It took me a very long time before I realized my problems were not the ignition upgrade, or a rash of "Bad" ECM's and coils. It was the wires all the time!

One other item: It may be your setup is "Too Lean". Check the basics (Probably not the carb because it is still doing this using a different unit) Fuel filter, clogged/corroded fuel line?

Double check TDC. You may have skipped a tooth or 2 on the timing chain. Rotate to the TDC timing mark, pop off the distributor cap, and look where the rotor is pointing (SB at #1 spark terminal, or 180 degrees.)

Hope this helps! Good Luck!

[charger1970]

Plum Cuda,
I recently bought a 670 Advenger carb that caused me the same problem. I called Holley and they told me to put bigger jets in it because it was running lean. Didn't work. I found a old guy who worked on carbs for 30 years and he adjusted the air/fuel screws and it ran like a charm without the backfiring or hesitation. I attempted to adjust the carb myself for hours on end and just couldn't get it to run good. I don't know how he did it but he said you have to adjust it cold and do it by ear. Good luck.

[cudacarl]

Sounds like you had a problem that may have screwed up your carb. Years ago my cudas vaccuum advance can broke and advanced the timing all the way the second it sensed even the littlest bit of vacuum. It sounded like a drive by shooting but it didn't hurt the carb. Try running it with the vacuum advance plugged at the carb and see if it backfires.

[mr.b]

the backfiring through the exhaust may be do to bad plug. i had replaced all my plugs once and then drove my car. it backfired like crazy esp. at highway speeds. it was aweful. after doing several things i decided to check the plugs again and the #2 plug picked up a huge piece of carbon stuck in the electrode. cleaned it and it ran great.