I'm getting a positive fuel backflow through the tank vapor line to the canister flooding the canister and spilling on the driveway. I'm have been running off my right side tank because the left will is not working for some reason. I removed the tank filler cap off the right side tank but the fuel flow continued then I removed the tank filler cap off the left side tank and heard an audile "whoosh" of pressure release. The fuel flow to the canister stopped but after a bit fuel began pouring out of the left side tank filler neck all over the drive. I cut the engine off. and washed down the drive. I'm out of ideas. I replaced the original 30 yr. old canister with a new one but no help. The truck is entirely original with all the original plumbing and wiring.