Gas Tank - vented or not

[81 ZXT]

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?

[sblake01]

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.

[sblake01]

Turbo and non turbo would be the same where emission controls are concerned. Here's a link to the FSM if you don't already have one:

http://www.xenons130.com/files/1981%20280zx%20FSM.zip

In case you need the turbo suppliment:

http://www.xenons130.com/files/1981%20280zx%20Turbo%20Supplment.zip

[81 ZXT]

Thanks, Stephen. I have read through the FSM and will perform these checks this weekend. I'll let you know what I find. Thanks again for your help.

[81 ZXT]

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.

[JKiggans]

My 280zx does the exact same thing, what i do is when i first start it up let it sit for a few seconds and rev it usually theres some back pressure once it gets out, she runs just fine

[sblake01]

And you're okay with that? If it were me I'd figure it out why it does that and fix it.....