Fuel Filling and Venting

My car had an issue with a fuel smell in the garage and cockpit. The tank vent was a simple line that went up above the level of the tank and then down to the bottom of the frame.

The smell was corrected with the addition of a valve Fuel Cell Pressure Relieving Vent Valve, In-Line, 6AN Male | Pegasus Auto Racing Supplies which allows pressure to escape if it builds up to a certain point, and allows air freely into the tank as fuel is consumed.

The problem is that when filling, the air doesn't build up enough pressure to trip the valve; instead, it tries to burble out past the fuel flowing down the fill tube, splashing fuel and slowing things down. At some point during the fill, a slug of fuel becomes stuck in the filler neck. This surprised me, but the cause was confirmed when I opened the connection above the new valve and there was a "whoosh" of released air and the fuel in the filler neck vanished down into the tank.

Clearly, there needs to be a venting system that will allow air to freely escape the tank when filling, but not freely escape when sitting in the garage. Some production cars have a vent line that runs up to the neck of the fuel filler (the tank funnel), but the Sparco funnel and cap assembly that came with the kit does not have a provision for this.

I'm thinking of adding a bung to the Sparco funnel like this one http://www.fillernecksupply.com/jeep-fuel-filler-vent-hose-nipple-see-applications-cjfhn1/ with a Tee into the vent line upstream of the valve, but don't want to reinvent the wheel. Has anyone found an alternate solution that might be better? Or a bung that will seal against the curve of the Sparco funnel?
I have a roll over valve mounted on engine side of the firewall about 2” from highest point possible. Never noticed an issue.
I have the fuel vent hose running from the top fitting on the tank end to the fill hose, just above the tank it is then attached to fill hose up to Sparko tiller. I have a fitting for the hose into the Sparko just above the fill hose level. This works just fine I have no filling problems, no smell problems and no fuel feed problems.
I mounted a roll over valve just above the tank on the engine side of the bulkhead with a K&N breather filter on the end. This is similar to the setup I had on my drag truck as well as on my hot rod - never had an issue and they are both garage kept. They both had the check valve built into the fuel cell, but is is similar to the -6AN version I bought for the SL-C. I know some have used a charcoal canister like the OEMs to keep the smell down, but I never needed it.

Terry Oxandale

Skinny Man
I run a typical roll-over vent (ball stop) to a hose. I do occasionally get the aroma...err the odor, of gasoline periodically, but typically during a large change in temperature that causes the tanks to push vapors out.
I also used a roll over ball vent. But, I installed a spring so that there was very minimal (like a few ounces) seat pressure, keeping it constantly closed. Expansion can still be taken out in the rubber filler neck (which would be minimal anyways), and low pressure from the tank emptying will easily overcome the spring seat pressure. It acts more like a one way valve now only allowing air in. Tube running off from it exits under car.
I decided to add a "T" (Fragola Performance Systems Tee Adapter Fittings 482506 - Free Shipping on Orders Over $99 at Summit Racing) into the existing vent system, above the valve (see my first post, above), with an adapter (Derale NPT To Nipple Fittings 98104 - Free Shipping on Orders Over $99 at Summit Racing) to a regular 3/8" fuel hose/vent line, which runs up to the top of the firewall and across to the other side of the car where it pushes on to an aluminum 3/8" tube (2024T3 ROUND DRAWN from Aircraft Spruce) which is welded to the Sparco fuel funnel.

Welding to the fuel funnel requires someone good with a tig welder (not me!). There is some kind of coating on the fuel funnel which doesn't like to be welded, and it is pretty thin aluminum, however the end result turned out quite well. We put a small shim on the inside made from 1/16" flat stock hardware-store aluminum, to provide a heat sink and help reduce the chance of blowing a hole through the funnel while welding.

When the Sparco cap is on, this vent is sealed into the system. With the cap off while filling, the air is allowed to escape from the fuel tank, passing the gas station filler nozzle, preventing splash-back and increasing the speed that fuel can be put into the tank. The tank can be completely filled, to the point where fuel is visible sitting in the filler hose.

I still find that I can only hold the trigger on the gas station pump about 3/4 of the way down without the occasional trip, but am still playing with holding the nozzle at different angles, so this might improve.

Bottom line: the new vent is a big improvement over the old system with just the vent valve in the line.


I noticed a picture of Graham Hill standing beside a GT40 with the front clip open and next to the filler caps were two small objects which I had not seen before so I looked in the book Ford GT40 Production and Racing History individual chassis record by Trevor Legate and in the exploded view section on page 202 it shows the complete fuel system including valve none return units ( key number 5 part number 106292) I am not sure if these valves were fitted to all the cars or perhaps just the road cars but I made a pair and they work great.