noticed a bit of air pressure when taking off cap after running for 5 minutes

im running efi engine standard tank with a surge tank setup

with a brand new petrol cap

does it need a breather in the cap or something
or
is it ment to be pressurised

thank you

my 180sx would have a lot of pressure when opening on a hot day after running

and my bros corrollas fule tank imploded one day at the drags lol

hope that helps some how

no..there should be no pressure. late model cars have a line from the top of the fuel tank to the engine bay, that goes through a carbon cannister, and feeds fumes into the engine at vaccuum.

1200 tanks should have a breather to atmosphere. you can't rely on the cap.

any ideas any1
dont realy want to run a canister

so is it dangerous???
should i leave it loose???

???

has any1 done this before???
did you run a breather???
And where???

thank you

i had this problem with my ute.. never solved it... was going to drill a breather hole in the filler cap but never got around to it

there is a breather system on the tank which goes up into the guard, you should be able to access it through the panels in the tray. maybe it's blocked, or maybe just inadequate. tank should be able to breath one way or another

the breather hoses are blocked or missing. A non-EFI system has less fuel leaving the tank at a time, so you may need to upgrade the diameter of the breathers. Make sure they are still connected. All in the factory workshop manual, and discussed before (with pictures I believe:

In the wiki:
Fume Control: Datsun 1200 wiki

Every car I've ever put gas in here in Japan does this, so it can't be all that bad. I thought it was wierd at first because I've never noticed it in the states, but when every car (except diesels, for some reason) over here did it I just got used to it.