small constant backfiring out of exhaust

[barryv]

hi, i have a 72 barracuda with a 440/4 speed.   i have had this car for a few years but just got it on the road. it has fresh gas etc. i always seemed to have a small miss that i never figured out . yesterday i took it for a 5 mile ride and car started running rough and popping out of exhaust .i tried a different carb today and still pops out of exhaust while i rev engine up in neutral.timing chain i replaced when i got the car a few years ago. how do i know if there is a engine problem. i sprayed soapy water around engine but did not notice any vacum problems. any suggestions would be appreciated,thanks

[MEK-Dangerfield]

Possibly a leak in the exhaust system.   

Are the headers/ exhaust manifolds tightened to the heads? If you are running headers, maybe a leak at the collectors?

[brads70]

What's the timming set at? I'm wondering if you need to advance it?
Points or electronic ignition?
wires and plugs new? wrong heat range?
any exhaust leaks?
My gut feeling...Sounds like timming is an issue?

[quapman]

Are your 5 & 7 wires switched?

[barryv]

timing was set about a year ago and  i havent touched it. it has headers.it doesnt seem that the  header bolts are loose but i will check.ignition wire order hasnt been touched.wires could be an issue.there not new but i took them off my other mopar all of the header tubes seem hot  when i touch them briefly.any other tips, tanks

[Chryco Psycho]

Where is the timing set to , I would set it at 36-38* @ 3000 rpm , leave off the vacuum advance & run approx 12-14* at idle ?
are any of the plugs fouled ?
any leak in the exhaust system where air can be pulled into the exhaust can cause a igniton in the exhaust

[mickey]

If all other suggestion pan out, possible bent push rod.

[barryv]

i have to buy or borrow a timing light. i will check exhaust leak were header bolts up. it doesnt sound lile a header leak at the flange area. i might take the wires off my roadrunner to see if that helps.whats the best way to check for vacum leaks,thanks

[Chryco Psycho]

you can mark the damper 2 3/8" ahead of TDC , that is 36*
 I ususally pull one wire at a time off the dist cap to see if every cylinder is working as hard if not you will know where to look if one or more cyliders seems to not have any or little effect with the wire off

[barryv]

i will try the wire idea off the distributor .maybe i have a bad wire or plug,thanks

[Supercuda]

Many people use WD-40 for vacuum leak diagnosis. It temporarily seals a leak, raising (or lowering) the rpm. I prefer using starting fluid, as it ALWAYS raises the rpm, and only raises it where it is sucked into the leak. If you use ether, use care, as it is explosively combustible. Use it sparingly, and be careful not to generate a "false positive" by accidentally feeding it into the carb throat.

[HP2]

I've heard of problems like this when people convert from manifolds to headers.  The new efficiency of the exhaust leans out the fuel mixture and things start popping in the exhaust.

I'd also second the look under the valve covers for a bent or dislodged pushrod or other related valvetrain issue.

[barryv]

i think this is going to turn into a bad weekend looking for the problem.hopefully i will get lucky and it will be a minor fix,thanks

[barryv]

today i tried a few things .i think i may be going in the right direction. i tightened up all header flange bolts and flanges were the end of header goes into exhaust pipes.the small backfiring noise went away. i still have a miss which i have had for a long time. i sprayed carb cleaner with engine running along edges of intake manifold and noticed a lot of bubling on the drivers side and a little on the pass. side. i am not sure if idle changed when spraying the carb cleaner but it was definatly bubbling. would that mean i have a vacum leak. thanks for the help

[Chryco Psycho]

no bubbling could be just heat from the crossover under the intake