Gas cap not venting

Joined
Jun 2, 2005
Messages
142
I recently bought a new gas cap (when I bought it, it had an incorrect locking cap with no key so I yanked it off) from Spector, part #168-01C for my 72 FJ40. Now, when I start it up, about 5 seconds later I hear the gas tank make sort of an oil can noise. When I shut it off, 5-10 seconds later I hear it again. Turns out the cap isn't venting, and is causing a suction. If I leave it running, and pull the cap off, the idle drops just a hair, and when I put it back on and the vacuum returns, the idle raises just a few rpms I'm assuming because it leans out a bit. These gas caps ARE supposed to vent, right?
 

yotanut

 
Joined
May 15, 2004
Messages
285
Location
Tucson
The cap is not designed to relieve pressure, but let air in. The cap usually opens to"vent" at .9 to 1.8 in. vacuum. If your charcoal canister is plugged, this might be your problem.
 
Joined
Jun 2, 2005
Messages
142
yotanut said:
The cap is not designed to relieve pressure, but let air in. The cap usually opens to"vent" at .9 to 1.8 in. vacuum. If your charcoal canister is plugged, this might be your problem.
That's the problem, there is a lot of vacuum , enough to suck in the top of the gas tank because it is not letting air back into the tank. When it's running and I start to pull the cap off, I can hear the air rush in and it tries to suck the cap back on. If it's supposed to have that much vacuum that's fine, but I just don't want it to get starved of fuel and lean out and burn a hole in a piston or anything... The noise the tank makes is annoying too. Just bugs me.
 
Top Bottom