Suitable Vapor / Over fill valve for retrofit

Hello everyone!

I am an FBBO guy (same username) but have had 67, 68, and a 69 Darts in my younger days.
A few years ago, I retrofitted a 68 Satellite based on slantdixdan's fantastic article at Allpar. It worked great but I now live in the foothills of Los Angeles with lots of hills. After an almost full tank, the gas from the tank vent got into the carbon canister in the engine compartment since there was nothing to prevent the gas from entering the canister from the vent line while going up and down hills. So, what I did not think about was how do I replicate the vapor separator portion / over fill check valve part I see in later 70s A/B body diagrams.

What do you recommend in between the tank vent and the carbon canister to prevent gas from getting in carbon canister?

I know that there is GM product for old vettes and modern Fuel Discriminator Valves. The GM fuel vapor separator valve part number is 353162. There is also a Discriminator Value DV100 from Fuel Safe and I'm wondering if that works as an overflow/gas valve as well.

Any help or A Body part model part that I am not aware of would be a great help! This has been a four year journey for me. Prior to moving California, the retrofit worked great. But since moving here almost overfilling my tank, I never thought about needing a gas/vapor valve.

Thanks and any help is welcome!

That GM № 353162 ought to do exactly what you want. A detailed description of its function is At the gas tank a fuel separator valve is bolted onto a bracket near the top of the tank. A 3/8-inch hose on the bottom of this valve connects to a vent tube on the top of the tank and a 1/4-inch hose at the top of the valve connects to the steel tubing [that runs forward to the charcoal can]. The fuel separator valve has a float inside that closes the valve when liquid fuel floods the valve. This can happen from fuel sloshing in the tank or if the car is parked at an extreme angle. The valve prevents liquid fuel from entering the tubing and overwhelming the storage ability of the charcoal can. Obviously, being a float-chamber device, this valve has to be mounted topside-up.

It does not look as if the DV100 item will do what you want, and it would be a much bigger pain in the nuts to mount.

If you want to finish the job of closing the fuel system all the way completely, you'd want to adapt a '71-up pressure-vacuum fuel cap, and eliminate the vent tube that runs from the top of the filler neck to atmosphere. That's relatively easy on something like a '68 Dart (swap in a '72-'76 fillpipe and you're done). But it would be a major undertaking on something like a '68 Satellite (no same-body '72-up vehicle to get a dimensionally-correct fillpipe from) so instead, just reroute the end of that fillpipe vent tube. Presently it runs up about as high as the trunk allows so liquid gasoline all but can't get out, then makes a U-turn and goes back down, through the trunk floor, and just ends vertically under the car. All you have to do is connect that open end via fuelproof hose to a T in your vapour line running from your (new) separator valve forward to your charcoal can.

For those who don't know what in the Screaming Yellow Zonkers we're talking about: stopping an old car making its vicinity stink of gasoline. The retrofit info Mrmolding is talking about is here.

Thanks!!! I have confirmation of what to do! The 68 satellite does not have a vent tube on the filler neck. It has two short flared vent tubes coming out of the tank. Originally, both tank tubes connect via hose to two lines that vent to open air. One tube goes up and back down and the other goes up in the trunk and back down into the frame rail.
In my retrofit it teed the connections from the tank into one and connected to the line that went to canister along frame next to fuel line. But now I’ll put the gm part in between them after my tee. Makes sense. Thanks again!