Happy Easter All...
What are the thoughts on a check valve for the gas tank vent line?
The reason for the question is I have a poly tank with a return port (I assume for fuel injection return) and when I plugged it the truck would run like crap due to a vaccume lock, I then put on a length of fuel line to act like a vent and all runs great....the problem is that when I fill the tank I get a strong gas smell, even when the trucks sits in the garage overnight...no leaks anywhere. I was thinking a check valve would allow transfer of air IN but not allow fumes or fluids OUT?
what do you think? Does anyone have a particular setup they can suggest?
thanks, Ed
ps, 15 gal poly tank, 1/4" line to ford\holly 2bbl. carb on 239Y

 

It needs to breathe both ways. How about putting a charcoal canister on the vent line?

It sounds like you are using a non-vented filler cap. If you go to the proper cap, you could plug the vent line connection.

 

the tank vent/rollover kit from MF

REMOTE ROLL OVER VENT VALVE, this is the best choice for all
1953-55 and underbed tanks . . . . . . . . .1641 . . . . . . . .$15.00 ea.
REMOTE VENT INSTALL KIT . . . . . . . . . .1641-K . . . . . .$10.00 ea.

page 60 of the 2009 catalog

has a check valve in the vent head. this lets expansion out, but stops wafting.. this completely stopped the gas smell for me.

sam

 

I had the roll over vent tube in mine before I moved it under the bed.

 

Use a roll over valve with a provision for attaching a length of fuel line to it. Terminate the line with a charcoal canister or a fuel filter. As long as the truck is upright the vent will pass air both ways, it only seals if the truck is upside down.

 

Just plug the vent line and install a venting gas cap - that's all you need.

 

Then the smell will come from the vented cap?

Chuck

 

right.. the MF install kit comes with the filter and hose..

and my vented cap really stunk the place up before that..
(69 stang vented cap)..

sam

 

Sounds like the roll-over kit is what I need. I got the tank from MF and should have gotten the kit then, I have a real nice locking cap but it's not vented. Thanks for the replies....I'll get a kit on the way.
Ed
ps....The fuel purchased at the "Spinx" stations here in S.C. STINKS worse than anyone else's fuel....? They must have a different additive in it..?!

 

I have run into the stinky gas as well. I believe they are using a cheaper additive and/or chemically boosting up the octane of a lower grade of gasoline.

 

I'm not exactly sure about how your tank is set up. But the only time you should be venting fumes out of the tank is if there is pressure inside. And th eonly time that should be happening is when it warms up un the mornings and there is a fairly good temperature change (like from the 30s to the 60s).

When you are driving the truck there should only be a slight suction and fresh air pulled in to replace the gas being pumped out. So unless youhave this tank sitting outside and it goes through a lot of temperature dynamics, like the sun shines on it during the day, you shouldn't be getting much if any smell out of it at all.

And yes, if it has to vent then the outside - at the cap is the place for it to happen. If it vents too much for your comfort then try the RO kit.

Also if it's that strong then you need to check the filler neck connections, the fuel line, and your sending unit seal.

 

I really don't have a problem. I have a filter in the vent line ( rear 17 gal tank ) and it works fine. Some slight smell but it's a old truck and gas in a open container (open vent even with a filter) will smell. If it bothered me I would have a charcoal canister, but enough this was e william question not mine. Bye have a wonderful day.

Chuck

 

Hi Julie,
The setup I have is a MF 15 gal. poly tank that replaces the stock unit under the running board. When I had the second port on the tank plugged I had terrible throttle responce, It would idle and run at full throttle on the highway but would chug and lerch while trying to accelerate...I was in Pigeon Forge at the time and hours from home. Got home and put a vent line on the second port and all the troubles quit.
The second port I assume is for fuel return in an injected system? I think I'll try to setup a fluid check valve to keep gas from running out the vented port when overfilled and run that into a filter cannister to arrest some of the fumes smell.
Other than this I'm real pleased with the way the old truck is running. Still running the original 239-Y and the 94-ford script carb.
thanks for all the input, I'll try to let you know how things go when I make the changes.
ED

 

A simple and inexpensive check valve can be had in the disguise of a basic PCV valve. Test the valve by blowing/sucking on one end to see which way is open and which is shut off. Put a vent hose on the tank and install the PCV valve in a vertical orientation higher than the tank top so gravity is shutting off the valve, but it opens with pressure applied to the open end. Now even if you overfill the tank the valve will shut off and not release gas or fumes, but the slighest reduction of pressure in the tank will open the valve allowing air into the tank.

 

Yep it's just not venting enough and there is a "vacuum" being created in the tank under high fuel draw conditions that the fuel pump can't overpower and is starving the engine of fuel. It just needs better venting.
Just as an interesting note, I have a Carter X type fuel pump on my 390 and when I run out of gas, it sucks so hard it pulls in the sides of my gas tank - it sounds like someone is behind the seat (51 F1) hitting the thing with a baseball bat! Scared me to death the first time it happened!
But even with that kind of fuel draw (to a Edelbrock 750 on a 390 FE) the vented cap I use is good enough!

For your set up, a well vented cap may do it, but AXs idea below is a great one (as usual). I might tend to use both because you will need a little pressure relief as well, as the tank and gas warm up during the day.

Here in San Diego, we have spring and fall days where the night time temp will dip into the upper 30s but the day time temp is in the 90s (it's the desert thing) you will get a fair bit of expansion/pressure under conditions like that, and will probably smell some lite fumes venting out the the cap if the truck is idle, but that's normal - a little bit of fumes - not over powering like spilled gas.

We also have to be careful here to not overfill our tanks up the spout, especially early in the morning when the gas comes up out of the ground cold. By the afternoon it may be dripping out the spout!