My Gassy-Smelling 71

My Dart is a 71 as well. Tried everything to get rid of the gas smell including adding a charcoal canister, new gas cap grommet, new rubber hoses. I can almost promise you the issue is with the gas tank and/or vapor canister in the trunk. It's just a bad design that's prone to leaks. My car is rust-free and even then the vent fittings coming out the drivers side of the tank (theres 4 of them) leaked fumes where they inserted into the tank. The vapor canister gave off fumes as well. Also the rubber hoses which connect the vent fittings to the fittings on the vapor canister are a PITA to change, and most likely cracked due to age and leaking as well.

I finally just replaced my tank with the 72+ style (Spectra CR11E) which allowed me to eliminate the vapor canister. The 72+ style has a single vent fitting at the top-front of the tank which can easily be spliced into the hard vent line which goes to the passenger side fender in the engine bay. No more fumes, fixed 100%. I don't even have the charcoal canister anymore and there's still no problem with fumes.

If you do decide to swap your tank to the superior 72+ style you may want to consider at the same time changing the filler neck to the 72+ style since those gas caps are readily available. Better yet get a 75-76 filler neck which is the unleaded style with the better anti-spashback design.

I seriously wouldn't even waste time messing around with the 71 tank unless you're trying to keep your car exactly original. Hook it up to a smoke machine and you'll see the leaks for yourself.