Fuel Tank Vent

[Jusjofok]

Hi guys, new to the forum and the world of Z's.

Ok so here is the deal, have a 72 240Z, has mechanical and electric fuel pump, the PO installed the electric fuel pump in the place of the fuel filter. I am in the process of doing the wiring mod to install the pump at the tank where it is supposed to be.

Now for the knowledge tapping part, the tank does not seem to be venting, I drive the car about a mile and the car will die and the fuel pump will rattle (like it does if it doesn't have any fuel in it), I can leave the key on and go back and open the fuel tank cap and it will suck in air when I take it off and the fuel pump will quiet down as it draws fuel. My question, is there a vent line for the tank or is the cap supposed to be vented? If there is a vent line where does it pull its air from and are there any commonly plugged areas?

Thanks

Justin

[MikeW]

Hi guys, new to the forum and the world of Z's.

Ok so here is the deal, have a 72 240Z, has mechanical and electric fuel pump, the PO installed the electric fuel pump in the place of the fuel filter. I am in the process of doing the wiring mod to install the pump at the tank where it is supposed to be.

Welcome.

For 72 there was only a mechanical pump. The electric pump near the tank was added to later models.

[Carl Beck]

This should give you a clue...

As you can see there are 3 vents on the tank - all of which go to a Gasoline Vapor Recovery tank - that tank is then vented via #46 to the front of the engine compartment.

No - the gas cap is not vented. It's a sealed system to keep gasoline vapors captive.

FWIW,

Carl B.

[citjet]

Ok so here is the deal, have a 72 240Z, has mechanical and electric fuel pump, the PO installed the electric fuel pump in the place of the fuel filter. I am in the process of doing the wiring mod to install the pump at the tank where it is supposed to be.

Welcome Justin, from another newb...

Here is a diagram of the stock fuel system for a 240.

You may want to check what pressure your electric pump is putting out, anything over 5 psi will not be helping you 3.5 psi is more ideal. Are you still running both fuel pumps? I'm not sure if the mechanical pump will like receiving fuel under pressure, someone with more experience will have to chime in with that.

Carl beat me to it.

240Z Fuel System.pdf

[Jusjofok]

Thanks Carl, so from the picture i am guessing the vent line ends up near the smog pump on the left side of the car? My smog system is inoperable so I guess if it were to be plugged it would be somewhere around there or should I look at the purge tank first?

Thanks

Justin

[Weasel73240Z]

Justin,

I don't know what your carb setup is, I assume your running round top SU's. With that set-up, you probably don't need the electric pump, especially in Kansas. The electric pump was added to help with vapor lock, which is probably not an issue in cooler climates like your (or mine). I run the mechanical pump only with ZTherapy carbs, and it runs fine.

[Jusjofok]

CitJet, fuel pump pressure is fine, when it dies there is no fuel at the pump up front, I can either take the cap off the tank and it will pull in air OR I can take the suction line off the elec fuel pump and it will pull air back to the tank from there. BTW, I like your avatar and handle, I work for Cessna.

Weasel, carbs are stock round top SU's, I am thinking as soon as I get the tank to vent correctly the electric fuel pump won't be necessary.

So where does the vent line connect up near the carbs? To the air cleaner housing? Smog system?

Thanks

Justin

[geezer]

Here's another illustration that may help you connect it the way it was originally.

[beandip]

Thanks Carl, so from the picture i am guessing the vent line ends up near the smog pump on the left side of the car? My smog system is inoperable so I guess if it were to be plugged it would be somewhere around there or should I look at the purge tank first?

Thanks

Justin

There is a fresh air/vent line that runs from the gas tank to the evap tank. It exits the tank just above the sending unit for he fuel gage. Then it exits the Evaporation Tank , evap, and goes forward to the driver side of the engine where it is attached to a three way valve , Brass and it has one inlet one exit to the air cleaner and another attaches to the breather coming out of the engine block. These are all about 3/8'' hoses. What the brass valve does is it allows air to flow into the gas tank from the clean side of the air cleaner, and then when there is pressure in the gas tank from expansion on a hot day, it vent into the engine. So look for a small hose back above the sending unit. By the way , your Z is already wired for a electric pump back by the tank. Follow the wires going to the sending unit back up toward where it comes down from the floor. Find a couple of wires one green and one black , rolled up and taped with blue tape . This is what they are for. Black is ground.

Gary

[Jusjofok]

Ok guys, thought I would report back to you. I found the 2-way check valve to the left of the air cleaner housing, I took it off and when I pulled the line off that goes to the tank it pulled in air The check valve did not operate when I blew/sucked directly on the valve, a little bit of carb cleaner and a few minutes later the check balls were working as intended. I went for a drive and everything works just fine now

Now I just need to work out the stumble just off idle when under load...

Oh, I have found all the associated wiring for the fuel pump behind the dash and at the tank, I will be installing a 20A circuit breaker instead of a fuse and solder the feed wire onto the black/white wire at the back of the fuse panel, you guys have any other recommendations?? Like maybe a relay that uses the power from the black/white wire to make and the feed wire would be the big white wire from the starter?

Thanks for all your help guys, it is much appreciated!

Justin