Fuel Cell Building Pressure

[gcb17]

I've got the cheap Summit Racing 15 gal plastic fuel cell in the back of my CJ7, and it was building a lot of pressure while I was driving it around today. I have one of the bottom outlets going to the carb as a fuel feed, and the 3rd outlet on the fuel filter (at the engine) acts as an overflow to the top of the fuel cell through another hose. I think my engine is pushing a lot through that "overflow" outlet on the fuel cell and causing a lot of pressure to build up in the fuel cell. I think my cap is supposed to be vented (http://www.summitracing.com/parts/SUM-290198), but maybe it's not working right? What else could the problem be?

1979 CJ7
AMC 360

 

[notajeep]

The top fitting on your cell should be the vent. You need a "rollover" valve there. Pretty sure you can get them through summit.

 

[jswainthug]

The top fitting on your cell should be the vent. You need a "rollover" valve there. Pretty sure you can get them through summit.

This is right. They sell a ball bearing kind that is opperated with gravity. There should not be any pressure with a rollover valve.

 

[Bart]

That tank is not vented and the cap should be, but is not. I had the same thing on my last buggy. I took the little vent off the gas cap thing and drilled 3 small holes in it. That vented better, but still not good enough. I ended up buying a roll valve and drilling another hole in the top of the tank to mount it, then ran a vent tube off of that. I'd go the second route and not put the holes in the cap. Just my $.02 worth.

 

[TonyM]

I run an in-cab 15 gal aux tank, that it completely separate from the fuel system. It should be OK for that tank to build pressure yes? It has a vent, but I only vent the tank when I need the fuel from it...

Sorry for the hijack, didn't want to start a new thread when this one was so closely related.

 

[Bucking Bronco]

Mine is a summit 16 gal and yes it did the same thing I also had one with the rollover valve and it leaked every time I was on my side or nearly virticle. It seamed the ball would not close off unless I was completly upside down.

To solve the problem with my new one I took off the filler cap turned it upside down and riped the little rubber flap that acts as the vent. It no longer expands but when I am upside down it leakes just enough to get the dirt on the tank wet.

 

[gcb17]

Mine is a summit 16 gal and yes it did the same thing I also had one with the rollover valve and it leaked every time I was on my side or nearly virticle. It seamed the ball would not close off unless I was completly upside down.

To solve the problem with my new one I took off the filler cap turned it upside down and riped the little rubber flap that acts as the vent. It no longer expands but when I am upside down it leakes just enough to get the dirt on the tank wet.

I tried the rollover valve, but I don't like the fumes or the fact that it'll leak all the time.

Is this the cap you have?

 

[notajeep]

that is the same cap that is on mine.

 

[Herzog]

I had to run a vent line on mine as well... but it would push fuel out the vent a lot of the time. I ended up adding a small t-valve on the vent line so I could manually vent the pressure off if needed. Still kind of a pain but better than leaking everywhere.

 

[Bucking Bronco]

Yes.

That piece that looks like it takes an allen key, is the vent. I can't remember if I had to remove it to pull out the rubber flap.

The vent is simply 3 tiny holes that have a rubber flap so it allows air in but when you go upside down it plugs it. the problem is when the gas pressure expands it presses the rubber flap against the holes.