Air vent hole size on charcoal canister cap?

[76was124]

Anybody know what size orfice there is in the cap that sits on the second top hole on a FI (81) charcoal canister? Mine was missing and when I plug the hole I get a large vacuum created in the gas tank. I don't know if there could also be a air/liquid separator, or 2 way valve problem, but I thought I would start with this first.

For now, I made a cap with a 1/6" hole, we'll see how that goes baring any suggestions.

Interestingly the cap seemed to solve a power loss issue I had at constant speed (surging) which would present as a large vacuum leak I guess..

[4uall]

Mine didn't have one when I got Fiona When I cover it my engine dies Going to watch this post

[RRoller123]

The cap doesn't seal tight, it is more of a dust shield. Air needs to move in there to allow for makeup air in the gas tank.

[4uall]

so it looks like i am good then

thanks for the info

[76was124]

The cap doesn't seal tight, it is more of a dust shield. Air needs to move in there to allow for makeup air in the gas tank.

Hmmm...my understanding is that it is a vent, but with a metered airflow ? Also, with it wide open, I definitely get raw gas fumes in the passenger compartment. Do I have a 2nd issue then that is causing the odor?

[76was124]

See metered comment by Brad Artigue in
http://fiatspider.com/f08/viewtopic.php ... ed#p202808

[NSFIAT]

When I bought my car (81 FI) the previous owner had filled the opening with silicone - presumably because it had broken off. I recently replaced the charcoal and to finish things off I took a cap off of a plumbing p-trap and sealed everything up. I used to have a large amount of negative pressure in the gas tank, but haven't had to deal with that issue after cleaning out the 2 way check valve underneath the car (large deposits of a grey coloured grease - no idea what it was). Should I drill a small hole in that newly installed cap?