Fuel tank venting question

[mattpatt]

Am I correct in assuming that the fuel vent hose is sealed when the cap is closed and that the overflow hose provides the needed venting while driving. And that the low location of the over-flow hose outlet serves as a roll-over valve to prevent gas flowing out of the tank after a roll-over. Just wondering.

Thx

Matt

[CHANMADD]

If the gas tank is perfectly sealed........when the fuel pump sucks the gas out of the tank.....it will eventually cause a vacuum in the tank creating more suction back into the tank than the pump can overcome.........So as the fuel goes out , air lust be allowed into the tank to replace the space the fuel took....some gas caps have a small breather hole , and others have a remote mounted breather.....or an in tank breather ......these breathers should be of the type that has a tipover valve that stops the flow of fuel out the breather if overfilled or if the car has a rollover accident......so you should have a breather with a tipover valve......

[mattpatt]

Thanks, Chanmadd

My question is what do I have in my stock SPF Mk 3 (#3033). Bought new from Hillbank. If there's any special valving it's gotta be in the cap. Does anyone know?

My interest in this is because I'm installing fuel injection and most of the conversion effort is near the tank. So, while I'm modifying things I thought I'd look at whether or not I should add roll-over protection if I don't already have it. If the fuel air vent hose is sealed with the cap closed and the over-flow provides the only means for fuel to escape in a roll-over I can just put the roll-over valve at the end of the over-flow hose. I think.

Thoughts anyone?

Thx

Matt

[WardL]

You haven't got much response on your question and while I'm not positive, I'm pretty sure this is the way it is set up: The gas cap seals when closed with no venting through the cap. About 6" below the gas cap there is an open overflow tube to the ground. You can look under your right rear fender and see the gas tank fill line and a small maybe 3/8" over flow line. You might call Hillbank and confirm with them. If you find the right roll-over valve let us know. I haven't heard much about that on Club Cobra. Hope this helps!

[mattpatt]

Thx, Ward.

Apparently, not many have thought/worried about this. I assume you are right that the small hose under the cap is probably the ONLY vent with the cap closed. Obviously, there must be at least one vent with the cap closed. If all of this is correct (???) a simple way to implement roll-over protection is just to extend the length of the over-flow hose so it is lower than the bottom of the tank - on roll-over not much fuel could escape. This would be an extremely simple and inexpensive way to add some safety.

Comments (from anyone, please) are very much welcome.

Matt

[WardL]

Wow! That is a great idea to extend the tube and somehow reinforce it to stay straight up. The other things to consider are what are the chances the tank is full when you happen to roll your baby? Maybe a tube slightly shorter than the tank bottom would be OK. Then what about if the Cobra isn't on flat ground and exactly upside down? What if the driver side roll bar makes the gas cap side of the Cobra the lowest side requiring a longer tube?

[CHANMADD]

Yea ...that is what I have ....a rollover ....at the end of the breather hose.....its mounted up in the rear wheelwell:.:.

[mattpatt]

Good comments.

Thx, guys.

Matt

[mickmate]

That's the way I plumb my tanks. I have a vent for the tank with a tipover or rollover valve sometimes straight on the top of the tank and the vent extends off that. I use a sintered bronze compressed air muffler for a vent cap so it breathes but isn't an open tube. We had some discussion about that recently if you do a search.

[mattpatt]

Sounds like installing a valve at the end of the vent/over-flow hose up in the wheel well is the way to go. Probably strap it to the fill tube.

Thx, again!