mlbinseattle

I had to pull the carb on my engine, and I noticed that the fuel kept trickling out of the fuel line where it connects to the carb. (I'm talking about after the carb was pulled ... not when the fitting was loosened.) It did this until I took the gas cap off the fuel tank. In the past, I've noticed that, when I get gas, I'll hear a "whoosh" when I remove the gas cap, so it is either pressure or vacuum being built up inside the tank. I've come to the conclusion that pressure is building inside the tank. If it was a vacuum, it would prevent the flow or "trickling" of gas out of the tank when the engine is off instead of aiding it.

Since there is a return line coming off the mechanical fuel pump going back to the tank, I would assume that the line should relieve the carb of any pressure at the fuel line connection which would prevent the "trickling of gas" when the fuel line is disconnected. However, if there is pressure building that's unrelated to the fuel flow out, then the return line from the pump should see the same pressure.

I know that the vent comes from the charcoal canister and associated plumbing back to the carb. I took compressed air and blew it through the line from the canister end (actually, after the check valve where the rubber hose connects to the steel tubing) to see if the line was clear. It is. I could hear the bubbling coming from the tank and see the fumes as well when I blew air through the line. If I knew how to test the canister control valve and the Purge TVS for that line, I'd do that, too.

So, the question is: Is all this normal, or should there be any pressure building in the tank? Seems to me if pressure is causing the trickling from the gas line to the carb, then the bowl would continue to fill until it spilled out somewhere. I did notice the inside of the intake was "wet" when I pulled the carb, but I've checked the fuel well plugs by letting the carb sit over cardboard with fuel in the bowl, and there was no dripping. Also, the plugs were sealed with epoxy when I rebuilt the carb.

None of this has caused any problems with the running of the engine. Am I imagining a problem?

sofakingdom

iTrader: (1)

Not really a problem... most every car will do that these days. Gas tanks are designed to keep the gas IN, whether liquid or vapor, PERIOD. No ifs ands buts or maybes; IN.

I learned some decades ago to pop the gas cap when removing the carb or disconnecting the fuel line at the rails.

mlbinseattle

Thanks, sofa. I figured this was probably the case, but it's always good to hear it from the ones with the knowledge and experience of these cars.