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Gas Tank - vented or not

81 ZXT

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1981 Turbo ZX - 21 gallon fuel tank. I have the car running pretty good (no missing) but at 3500rpm it hesitates like lacking fuel. I was really bad yesterday with less than 1/4 tank. I filled her up this morning and even though it still bogs down, it is 200% better than with 1/8 tank of gas. Question is: Is the fuel tank supposed to be vented? When I take the cap off after driving it goes psshhhhh. If it is vented, is it through the cap or somewhere else?

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You need to look through the emission control system section of the factory service manual. The carbon cannister/fuel tank vapor vent/vacuum release valve/check valve are areas to check for the problems you describe. It would be easier to read than to explain.

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Since the easiest check was to suck on the gas cap to check the checkvalve, that was the 1st thing I did. It seemed to work just fine. Then my son wanted to drive it so I said it's not running right but go ahead. He came back and said he did not see anything wrong with it. So I drove it and low and behold, it ran just fine. I have to assume that the checkvalve in the gas cap was stuck and I unstuck it. Life is good.

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  • 1 year later...

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