cant figure it out im desperate

[fryedaddy]

my 428 in my comet will fire right up and run.it backfires out the exhaust while im warming it up then it quits backfiring and sounds good till i pull out and give it some gas then it starts backfiring so bad you cant stand to drive it,but if you slow to a near idle it quits backfiring. help i have no idea,new plugs,wires,cap,rotor,tried 2 carbs.  still no luck

[GerryP]

It depends upon the sound.  A popping in the exhaust is an overly advanced ignition.  If you are running a vacuum advance, unplug it to see if that helps.  If you are running points ignition, you might try replacing the condenser but usually those are accompanied by poor engine performance, like bucking.

Is this something that just started happening all on its own, or did you do some work on it?

[fryedaddy]

its for sue more like a quick popping noise.my dist was corroded on the inside from sitting.i just took it out and put a new pickup in it and cleaned and lubed it and put my dist back in. and set my timing.im getting ready to try it out in a little while and i will see if that helps,my timing was a little high i backed it down to 33 total,bbm heads

[fryedaddy]

still doing it,i guess i have been having problems ever since i went from a msd box to a gm type module

[fryedaddy]

sounds like gun shots out the back two or three at a time. it will rev to the moon in neutral but going down the road it backfires as soon as you get over 3000 rpms

[Phil Brown]

still doing it,i guess i have been having problems ever since i went from a msd box to a gm type module

Put the MSD box back on it and see if the problem goes away

[fryedaddy]

still doing it,i guess i have been having problems ever since i went from a msd box to a gm type module

Put the MSD box back on it and see if the problem goes away

i would have to buy a new one$

[GerryP]

If there is a problem with the module, you will see it in the tach.  When an HEI module fails, it turns the ignition off and on.  The engine still runs, but has a bad misfire.  The tach needle will bounce around as it gets signal, then not.  You can buy one of those cheap $10 modules to swap out if you think you have a module problem.  Those cheap modules will work the ignition fine except they don't manage coil amperage and vary the dwell function.  Not something you would notice in many cases.

[fryedaddy]

i will get another module and im going to get a fuel pressure gauge and also the weights in my msd pro billet dist looked gummed up,maybe there not opening and closing properly if that would make it backfire i dont know.

[fryedaddy]

i may have it figured out.i remember when i put plugs in it a while back i tried one step colder plug than i have been running.i think they were too cold.three or four of them looked fouled, i changed them out with new nkgs like i have been running all along.i fired it up just now and no backfires so far but i have not been down the road yet

[fryedaddy]

i just got back home from taking a ride.fired it up it backfired once or twice while i warmed it up.i went down the road at 2-3 thousand rpms,ran fine,i squeezed down on the gas pedal and it backfired while revving,i was about to get aggravated with it then i started running it a little harder and it stopped.did not backfire any more on the way home even at high rpms?

[Stangman]

I guess see how it is tomorrow I was also thinking maybe a coil going bad

[BigBlueIron]

maybe similar issues similar to this on a new startup. One time would start and run clean rev clean next would spit and backfire like crazy. Lots of diagnosing and ultimately just swapping parts. Long story short it had something to do with the cap and rotor. Which both where new, switched to the duraspark cap/rotor and issue completely went away.

[fryedaddy]

Long story short it had something to do with the cap and rotor. Which both where new, switched to the duraspark cap/rotor and issue completely went away.

my disc cap was not on correctly.when i had my dist out putting a pickup in it and put it back in i clocked it different and the cap was 180 out and did not go all the way on. the cap  was about 3/16 too high and did not seat all the way down.i pulled the disc, i clocked the housing 180 and the cap snapped right on.now the rotor touches the dist cap button. my dist was not 180 out but my dist housing was

[fryedaddy]

i got it!! i took my 850 apart,i had sold it to a buddy who put it on a sbc and he had it rebuilt. someone had put #71 jets in it,it came with 80s at all 4 corners. i put it back like it was and its screaming now