74, Sniper EFI, Dual Tanks

Berta74

New member
Joined
Jan 11, 2021
Messages
2
Location
Texas
I have a 74 and about a 2 years ago I replaced the 4bl carb with the Holley Sniper. With the original tanks we tried to bung them together in order to use one in-line exterior fuel pump. It didn’t work. Then I bought the Holley 534-38 dual fuel kit made for this application. I pulled all the lines apart and plumbed per the diagram using, now 2, external fuel pumps. The distributor valve was placed under bronco and all wiring was done per the diagram. With gas caps on, selector switch toggled to rear tank (confirmed by hearing the rear fuel pump cycle on when key was turned), the bronco started right up. I let it idle for about 5 minutes, then gas started spewing out of the FRONT gas tank cap. Crawled under and seems like the rear tank is bone dry and the front is full. I have double checked the plumbing lines and about to get under and check electrical. I’m so lost. Why would the rear pump/tank be engaged electrically and run, but the return seems to be filling up the front. Any help you could provide is very much approached. Thank you.
 

Tiha

Member
Joined
Jul 22, 2020
Messages
106
Location
Midwest
Not sure about the External pumps you are using, but most likely the pump for the front tank has a bad check ball, if not equipped you need to add one to both tanks probably.

So with nothing to stop flow the rear tank is pumping the front tank over full.
 

Berta74

New member
Joined
Jan 11, 2021
Messages
2
Location
Texas
How would the rear tank be filling up the front tank? Shouldn’t everything be going through the selector 6-port valve?
 

Tiha

Member
Joined
Jul 22, 2020
Messages
106
Location
Midwest
I don't know what your selector valve configuration is, but it is either not designed to isolate the tanks or it is plumbed wrong.

So the rear tank running is pushing fuel through the valve and back into the front tank.
 

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