1970 Dodge Charger has backfire out of driver's side tailpipe - mechanic stumped

[matchek]

Hi, I have a 1970 Dodge Charger that has a backfire coming out of the drivers side tail pipe.   My mechanic is stumped.   Any ideas of what it most likely is.  I know it can be a lot of things.  When I give it gas , a loud bang comes out of the drives side tail pipe.

[b5blue]

Retard timing and test again?

[70 sublime]

How old is the engine ?
A valve not shutting all the way ?

[Kern Dog]

Your mechanic is an idiot.
These cars are simple if you have experience with internal combustion engines.

[cdr]

if its not an internal problem, The 1st thing that will cause that is fouled  spark plugs, ign plug wires firing order wrong, ign wires bad, dist cap cracked

[kent]

Process of elimination. I would start with firing order. Then move on to wires and plugs. Certainly in the timing.   

[birdsandbees]

Was it running fine prior?? 

[John_Kunkel]

Don't shotgun parts, hook it up to a scope.

[Back N Black]

Popping in exhaust, raw fuel and oxygen passing through through the engine and lighting off in the exhaust, misfire. I would start with a compression test before replacing any parts or adjusting timing or carb.
I had the same issue, did all the above and the last check I did was compression test. Number 2 cylinder was dead no compression, dumping fuel and causing backfire.

[BadA55charger]

I recommend also doing a quick visual inspection....pull off the valve cover on that side and inspect the exhaust valvespring for breakage.  I had a dual spring that broke the outer spring clean.  The inner lighter spring was fine and it popped out the exhaust on that cylinder. 

A quick on car replacement, and it was back up running great.