little help pls!

its a 1990 civic sedan, heres what I have.

When it gets down to 1/4 tank left it acts like it runs out of gas. Gas guage says 1/4 tank, and this is correct, I confirmed this at fill up, I can only put 8 gal. in, this is a 12 gal tank..........so indication is correct.

Also when it gets this low the car dosent exclerate like it does when full. when it does act like it running out of gas, I go and open the fuel cap and I can hear a big WHOOSING sound, like a vacum. I put the cap back on and it runs fine for a little bit, 5 miles down the rd, act up again, take cap off, WHOOOS! sucking sound, but then will run fine.

One I put a fulltank of gas it excelerates like normal and runs great.............untill I get to 1/4 tank.

so Im thinking vent line or something like that. with the fuel pump taking out the fuel, creating a neg pressure in the tank, the pumps having to work harder.

I have a hayens manual, but honestly that book is a piece of ****!!! it dosent show anything on the fuel lines, supply, vent return, nothing!

so does any one have any ideas on how to check the vent line or any other ideas?

Thanks guys