Mine has a non-vented on it and I was thinking of running a vented and doing away with the tank vent. Are any of you running a similar setup and what part number cap are you running?

 

Is your tank not vented? I would worry about fuel sloshing out the vented cap

 

You could do that.
The theory is simple, vented tank, non-vented cap. Non-vented tank, vented cap.
About the part number, Autozone says their number 6046 is vented, I checked the application for 67 a station wagon as I knew the wagons from that year have non-vented tanks.

 

Yeah I looked it up on Rockauto but the dimensions are slightly different from the stock non vented cap.

 

your tank should have 2 vent hoses, a thinner one, and a thicker one. you shouldn't need a vented cap, but putting a vented one on won't hurt anything. fuel does not slosh out through a vented cap, the vent is kept closed until a certain amount of pressure builds-up behind the cap-then it vents excess pressure. i would leave the tanks vents alone(rule number one: if it works-don't F with it).


bill

 

The vented cap does not relieve pressure within the tank it relieves vacuum. Currently I have the 2 tubes looped together with a steel tube connecting them together. I'm hesitant in putting the stock breather on there as all the folks who have used the cotton stuffed POS have had problems with it leaking and major fumes.

My tank and fuel system will hold a vacuum which I believe is effecting fuel flow to the engine.

 

yes, vacuum in the tank will affect fuel flow. you could drill a small hole in the steel tube connecting the hoses together to relieve any vacuum in the tank. that would be a very minimal source of "gas smell" with a small hole.


bill

 

I was thinking of that Bill. I was just wondering if anyone had swapped their cap on their 66/67.

 

what did you decide on doing Eric?....going thru similar siyuation

Ted

 

I had not played with it yet, been busy with some stuff around the house and working on everyone else's cars. What's with that?

 

I just completed a frame off resto and have noticed when I drive the car around the block, then remove the gas cap, there is a lot of pressure relieved.

1971 Cutlass Supreme Conv.

We removed the canister behind the back seat so I'm thinking I may need to do one of two things...

- buy a vented cap
- install a rubber line on one of the tank nipples to vent the tank.

I've yet to put the car on the highway, just driving around the block right now as I shake out any problems (still need a top and windshield). Just had the exhaust installed so I can drive her a bit.
What would you recommend???

Thanks,
-Lewis

 

I just completed a frame off resto and have noticed when I drive the car around the block, then remove the gas cap, there is a lot of pressure relieved.

1971 Cutlass Supreme Conv.

We removed the canister behind the back seat so I'm thinking I may need to do one of two things...

- buy a vented cap
- install a rubber line on one of the tank nipples to vent the tank.

I've yet to put the car on the highway, just driving around the block right now as I shake out any problems (still need a top and windshield). Just had the exhaust installed so I can drive her a bit.
What would you recommend???

Thanks,
-Lewis

 

I have not looked into this yet for mine as there has been other things more pressing. What you have in your tank is a vacuum condition, as the fuel is pulled out by the pump there is no air entering to replace the space. If its creating issues with the way the car performs then I would look into venting your tank by either reinstalling the stock system or something similar, or a vented cap.


The only time mine is an issue is at WOT in a about 1/8 of a mile, it'll stumble.

 

Lewis, the 71 used a vented cap. That's probably the easiest way to test your theory. Just curious though, on a frame off restoration why remove the vent cannister? It's part of the original build. I guess on the + side, you no longer are bound to the GM34R tank, you can use one from 68, 69 or 70?