FJ40 Dual Tank Fuel Problem

[FJ40RestoMod]

Hi everyone,

I’m at a loss and need some advice. I have a 1975 FJ40 with a Chevy 350 and an Edelbrock carburetor. The vehicle has been completely redone, and I’ve had dual tanks installed:
• New tank under the passenger seat (replacing the original).
• 20-gallon tank underneath the rear.

It’s running an electric Edelbrock fuel pump, a valve to switch between the two tanks, and (reportedly) one-way valves for each tank.

Here’s the problem:
After driving about 10 miles, the truck dies. I figured out that I need to prime the fuel line when this happens, but I can’t figure out why it’s losing fuel delivery.

Some additional info:

• Tank venting: The new 20-gallon tank has a gas cap with a pinhole for venting. The original tank (also brand new) does not have a pinhole.
• Charcoal canister: Has been removed/mitigated.
• I’m not sure if one tank might be pumping fuel into the other or if it’s vapor locking.
• The mechanic who installed it hasn’t been much help. He suggested converting to EFI, but even admitted that wouldn’t solve the issue if fuel isn’t reaching the line.

Questions I need help with:

1. What is the usual configuration for a dual-tank setup with an electric pump?
2. How can I tell if fuel is getting pulled from one tank into the other instead of going to the carburetor?
3. Is the venting situation adequate? Should the original tank have a vented cap as well?
4. Could vapor lock still be an issue with an electric pump?
5. Any tips for troubleshooting or fixing this?

I’m completely baffled and would appreciate any advice or guidance.

Thanks in advance!

 

[charliemeyer007]

My manual selector valve I installed under the drivers side section of the front bench seat, has 3 ports. The front tank is on tap when the valve points at it. When the selector points at the ground then the aux rear tank is on tap. The other port would be used to draw fuel from a tank in a trailer. When my aux tank goes empty the engine will "bark" and I move the selector to the front tank and continue driving usually without stopping.

My electric fuel pump draws from what ever tank I have selected.

Did your original set up have a return fuel line? Maybe they plumb into the wrong lines/tap. A small vacuum leak is all it takes in defeat a fuel pump. Depends on your fuel hose and routing for vapor lock.

 

[Paul_A]

I run two tanks located like yours using an electric fuel valve and an electric fuel pump and vented gas caps with no return lines. My pump is mounted near the front of the engine inside the frame rail at a point lower than both tanks so that gravity keeps the lines full of fuel. The pump sucks fuel from which ever tank is selected and up into the carb. If one tank runs dry I will hear a quick clicking sound as the pump is sucking air but once I add some fuel to that tank or switch to the full tank it picks right back up. As long as the cap is vented you won't create an air vacuum in the lines/tank. I had a car that had a plastic fuel tank and the draw from the pump started to collapse the tank due to vacuum in a sealed fuel system. More like a box of cheap wine with a bladder than a fuel tank. Once I opened the gas cap the tank reshaped itself to normal and it ran fine. Dodge dealer wanted a fortune to fix what drilling a small hole in the gas cap did.

 

[peesalot]

Have you checked the carb, bowl, needle, seat, what pressure is pump at ? All the stuff Paul A posted covers it well. The vents, yes a static vent on both tanks to a charcoal can vented to pre venturi air cleaner is ideal. On my dual tanks with no evap I T'd into the soft line for filler neck vent & ran a line back in the tub to rear corner where a vent line for rear tank come up thru grommet and both vent thru a line running up roll bar to a rollover valve and breather ( tiny one ) , I dont run a top.

 

[Mark Jennings]

You need to run vented fuel caps. On the early rigs, there is a ‘pin hole’ in the filler neck just below the fuel cap. For the rear tank, depending on the gas cap, there may be a check valve in the cap that lets air in, but not air out. What I found is the small electric pumps cannot pull enough static vacuum to open the check valve and you vapor/vacuum lock the pump. You will have to remove or modify that check valve.

As far as a leaking switcher valve, easy check is to fill both tanks, park on an incline…..if you see the downhill tank overflowing, the electric switcher is leaking. Believe me, buy a spare and a spare pump…..in the valve, the little o-ring that seals the valve is pretty wimpy and will fail…..and the best electric fuel pumps made can leave you stranded. I keep a set in my rigs tool roll……

 

[Paul_A]

Good advice from Mark, spare fuel pumps are cheap insurance.

 

[charliemeyer007]

+1 for spare electric fuel pump and filter(s). This is my 12 V $50 fuel transfer device. Will also do diesel. It is fused, switched and filtered, 5' suction and 20' delivery. Will attach to battery or cig lighter. This is the same pump I use in Elsie and my F150 both with carbs.

 

[FJ40RestoMod]

I run two tanks located like yours using an electric fuel valve and an electric fuel pump and vented gas caps with no return lines. My pump is mounted near the front of the engine inside the frame rail at a point lower than both tanks so that gravity keeps the lines full of fuel. The pump sucks fuel from which ever tank is selected and up into the carb. If one tank runs dry I will hear a quick clicking sound as the pump is sucking air but once I add some fuel to that tank or switch to the full tank it picks right back up. As long as the cap is vented you won't create an air vacuum in the lines/tank. I had a car that had a plastic fuel tank and the draw from the pump started to collapse the tank due to vacuum in a sealed fuel system. More like a box of cheap wine with a bladder than a fuel tank. Once I opened the gas cap the tank reshaped itself to normal and it ran fine. Dodge dealer wanted a fortune to fix what drilling a small hole in the gas cap did.

Hi everyone,

I’m at a loss and need some advice. I have a 1975 FJ40 with a Chevy 350 and an Edelbrock carburetor. The vehicle has been completely redone, and I’ve had dual tanks installed:
• New tank under the passenger seat (replacing the original).
• 20-gallon tank underneath the rear.

It’s running an electric Edelbrock fuel pump, a valve to switch between the two tanks, and (reportedly) one-way valves for each tank.

Here’s the problem:
After driving about 10 miles, the truck dies. I figured out that I need to prime the fuel line when this happens, but I can’t figure out why it’s losing fuel delivery.

Some additional info:

• Tank venting: The new 20-gallon tank has a gas cap with a pinhole for venting. The original tank (also brand new) does not have a pinhole.
• Charcoal canister: Has been removed/mitigated.
• I’m not sure if one tank might be pumping fuel into the other or if it’s vapor locking.
• The mechanic who installed it hasn’t been much help. He suggested converting to EFI, but even admitted that wouldn’t solve the issue if fuel isn’t reaching the line.

Questions I need help with:

1. What is the usual configuration for a dual-tank setup with an electric pump?
2. How can I tell if fuel is getting pulled from one tank into the other instead of going to the carburetor?
3. Is the venting situation adequate? Should the original tank have a vented cap as well?
4. Could vapor lock still be an issue with an electric pump?
5. Any tips for troubleshooting or fixing this?

I’m completely baffled and would appreciate any advice or guidance.

Thanks in advance!

I will take pictures of how it is set up in a couple of days. I wonder if the t valve is too high…it sits a bit high essentially almost between the front seats on the top seat rail….just higher than the original tank.

Rear tank gas cap has a pin hole and factory tank does not. Rear tank fuel neck does not have a return line. Front tank fuel neck does have a return line that goes back to the tank.