Quote Originally Posted by firebird77clone View Post
Put a pressure guage on the fuel line. Until then, your'e just guessing.

One thing to could do, - this just in... Crank it five seconds, then crack the line at the carb. If you get a squirt of fuel ( the pump should have a check valve ) then the problem is in the carb.
Sorry, but I cannot agree. If you have so much deterioration of an o-ring on the cap that it's coming apart enough to block the fuel filter it's a pretty good indicator that you've got some severe erosion of rubber components from the ethanol, very likely through the system where ever there's rubber. On a 1972 that's extensive as they were not built to be ethanol resistant. If you want to go on the cheap then after you do like Em (MelloYello) says and pump a pint or so of fuel from the carb inlet into a clear plastic/glass container (be careful, have a fire extinguisher present, normal fire safety precautions), see what you get in the container besides gas. You MIGHT get by with a new in-line filter and a carb kit, but if it pumps black particles from the line I'd be changing everything but the steel lines from back to front or you'll likely get stranded again when your new filter plugs. If you just rebuild the carb it'll very likely plug again, you just don't know when.