If the old cap was leaking, it was essentially vented (even if it was designed as non-vented when it was new). I mistakenly put a non-vented locking cap on my 68 Barracuda and it would draw a vacuum in the tank and gradually shut off gas after about 30 minutes of driving. I'm thinking the emissions caps started around 71/72? Does/did your 'runner have a charcoal cannister under the hood?

Last edited by GO_Fish; 06/11/12 07:51 AM.
Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph