Need Help With Exhaust Noise

[Bruzilla]

I'm hearing a banging sound coming out of the exhaust of my 74 Roadrunner. I've attached a video showing the engine running. It's idling smoothly and revs fine. But when I move the recording to rear, there's an intermittent banging sound coming out of the mufflers.

Is this a misfire? Did something crawl into the muffler? Any ideas?

 

[Ron H]

I'd try holding hand lightly or a sheet of paper against the pipes to see if that noise coincides with a change in exhaust flow. Sounds to me like engine has a tricked up cam in it, idles like it does anyway. Or if not some possible surging/stumbling? The change of flow could then be moving pipe hitting against frame or something. I reckon you may have checked this all out already loose clamp, pipe, ample routing over around axles, around shocks etc...

 

[dieseldazzle]

How old is your ignition coil? I had a bad one pop on me like that.

But off top I remember you screwed with the carb last and my rule is if a new problem pops up look at the last thing you worked on

 

[WileE]

Could be a sticky exhaust valve.

 

[khryslerkid]

Do a sparkplug inspection. Sounds like a lean burn pop. Check for a vacuum leak too.
You could open up the fuel adjustment a turn to richen it up and see if it goes away.

 

[moparnation74]

Lean for sure......better richen it up!

 

[mmissile]

idles very high...vacuum?

 

[Bruzilla]

Good call guys! I richened up the mixture and the banging went away. Thanks!

 

[PurpleBeeper]

Yay! Great diagnosis everyone

 

[Bruzilla]

Yay! Great diagnosis everyone

I've learned you get better results when you post a video where folks can see and hear what happens. That seems to work better than saying "it makes a noise that's hard to describe."

 

[Ron H]

Glad the carb adj worked for you. I'd take the tip posted about a vacuum check listening to your motor. My guess is you're running a higher idle RPM than should be and might be related to a vac leak or just adj your carb mix or tweaking idle adj a bit. Just my 2 cents tossed over...

 

[khryslerkid]

I've learned you get better results when you post a video where folks can see and hear what happens. That seems to work better than saying "it makes a noise that's hard to describe."

That really did help, hearing it in the video. You can't always hear the problem in some videos because of the quality of the mic or maybe too many other noises that might distort the real sound. I definitely could hear the popping in your video.

If you would have described the sound as you did without the video, we would have had you crawling around under your car looking for exhaust pipe clearances and tightening clamps! Lol

Many moons ago, I had a elderly lady bring her car into the shop, she said that the red light kept coming on. So I checked the sending units, temperature of the coolant, alternator output ect. It only had the one warning light but everything seemed to be ok.

She took the car home, (free of charge) called me the next day and stated that the red light had come on again.

(Now this is a talent that you aquire talking to many different people and trying to diagnose a problem that you can't quite put your finger on.)

I asked her, "what is the next thing that you do after the red light comes on?" She replied, "well I have to start the car again".

Bless her heart, she never said that her car was stalling. She didn't look at it that way. So I told her I would drop by her house the following morning to adjust her choke after the car sat overnight. That's all it was and she was great full.

A detailed description is very important when telling someone else your problem. If not, all you are going to get is 101 different solutions.