C3 fuel tank vapor emission system question

[Dale P.]

They say that there are no dumb questions ... so here I go

We have a 71 LS5 that is almost 100% orginal ... I know that there is a system that "pulls" gas fumes from the gas tank area up to and through a carbon filter by using vac. from the carb ( PCV system) .. I just noticed the other day that there is NO seal on the under side of the gas cap .. yet it is marked "sealed"
My question is should there be a gasket of some type on the gas cap under side
What happens if the vac line leading down to the carbon filter is "plugged off" and the gas cap is left without the seal .. The entire reasoning for the questions is that I smell gas fumes from the area of the carbon filter and I am thinking that the system no longer works as it should .. so I was thinking of plugging the vac source, leaving the gas cap without the seal and plugging the line that runs along the drivers side of the car UNTIL I can get all the parts to repair properly .. we are leaving from Bowling Green in 2 days and I don't have time to do any major repairs

[Patrick H.]

Re: C3 fuel tank vapor emission system question

Dale,

If you overfill your tank, you can get gas into the valve on the upper left portion of your fuel tank, and the gas will then travel to the carbon canister. It's one reason not to try and get that "last little bit" into these tanks. The valves (separation canisters) on the upper left side of the tank are also very hard to find in good shape, are not reproduced, and do wear out/break down.

New charcoal canisters are still available from GM, and Dr. Rebuild has the nice filter that goes on the bottom of the canister.

Yes, there should be a seal of some type inside the gas cap. I believe it should be rubber, but some have said cork. I'm not sure cork would have held up, but that's just my thought.

I'd leave the system alone, and just not overfill the tank. Fix it upon your return.

Patrick

[Tom R.]

[Dale P.]

Thanks guys for the details

The details are great .. at least now I will not need to be up the night before we leave under the car working on the ECS .. I feeel better about the drive to BG will the car as is ... I will be sure not to over fill the gas tank.
and I'll plan to replace the carbon filter when I return as well as try to find a rubber seal for the "sealed" gas cap ... any ideas on what the material was and the dimensions ??? OD x ID x TK

[Chas Henderson #28127]

Re: Thanks guys for the details

Dale,
Dr Rebuild. Part no. 3028201 original tan fiber, or fuel resistant nitrile rubber, part no 3028200. Both are $3.50.

Chasman