Help! Truck's not sucking up any fuel?!?

[Justin]

My fuel pump is good, as I checked it manually with the truck not running. However, it seems as though no fuel is being drawn up when the truck gets cranked over.

I tried sucking through the gas line (bad idea I know) and it seems as though there is more air than fuel coming through.

Which is odd, because I KNOW there is fuel in the tank,

Any idea's? I'm stumped!

 

Thanks! 

[datsunaholic]

Blow compressed air back from the filter inlet hose (with the cap off!).  Then see where the leak is.  Likely one of the hoses at the tank has rotted off.  Or the metal fuel lines have rusted away.  Last possibility is the pickup tube in the tank broke off, but the hose theory is the most likely.  They're a pain to get to, but you can reach them from the passenger side wheelwell. 

[southerncross]

cracked fuel line or a loose fitting somewhere would by my guess. you can take a small gas can and drop a gas line into it, attach that to your pump, and see if it runs.  if it does, keep moving down the line to the tank until you find the problem, which is probably a loose or cracked line given your description.  if it does not run, its from the pump forward.

[southerncross]

better yet use datsunaholic's method.  might be quicker than mine.

[metalmonkey47]

If you disconnect and plug the pickup tube on the tank, and plug one end of the fuel line, you can put some soapy water in a spray bottle, soak the fuel lines, and blow compressed air back through and have someone watch for bubbles. You can do it with the fuel line connected, but that's just my preferred method. 

 

Basically the same as datsunaholics method, but the addition of soapy water makes it easier to see small leaks.

[Dawa]

do you have any trace of rust in your filter?

[Justin]

.....  Last possibility is the pickup tube in the tank broke off, but the hose theory is the most likely....

Hmmm, I think it might be the pickup tube. When the tank is totally full, it seems fine. But when going uphill, or after having driven a bit, it starts to crap out.

 

Dawa- yea, my filters are constantly separating out the rust from the tank.

[Dawa]

my problem was similar to yours (same year/truck even) and it was caused by rust in the lines.

the rust made it all the way to and through my carb (weber) which blocked the jets.

i dropped the tank to derust it, blew out all the lines (rubber and hard lines,) and disassembled and

cleaned the carb

[converted_to_datsun]

Try dumping fuel in the carb and starting it a few times. Mine had this problem after putting the motor put back together. I primed the carb a few times and the third time It ran on it's own

[Aibast]

I had that problem - carb needle valve that lets  the fuel in didn't open. It was stuck because of dirt in it. At least on J15 the pump doesn't pump in fuel when it doesn't have anywhere to go. 

[Justin]

Yea, priming the carb enables it to run, so I'm thinking it must be the fuel tank pick-up line, mostly due to the fact that 

-it runs when the tank is FULL

-and it cuts out on me uphill

 

So I guess I gotta find a gas tank now...

[what]

Sure is cheaper that way though. ( Not sucking fuel ). :w00t: .

[.sunlover]

You can just pull the drain plug and put an elbow with a shut off valve and bottom feed that bad boy. Worked great on my 521.

[Justin]

Peeked out the tank, the pick-up line is fine.

Runs off an auxiliary tank fine.

No cracked lines are visible, or leaks or anything. Bed is currently OFF to check everything out. 

Still doesn't seem to be pumping as much fuel as it should, however.

Maybe a clogged jet in the carb??!?

 

This is so damn frustrating.

[Aibast]

I know, I'm going to change out the original J15 carby for a weber cos the floats needle valve is so worn that plays tricks on me. It gets stuck and then it doesn't seal again. so its No fuel or just to mutch fuel. It rearly stays on proper level.

 

First time it was stuck closed I also tought the pump is busted or the fuelline is cloged. But before that I had cleaned up the tank and but on a new coper fuelline from the tank. Good luck and I hope you find the problem area.

[Justin]

And, I guess on the forum I just need to refer to my truck as a '79.

[datzenmike]

A pump can produce almost any pressure imaginable but no pump no mater how powerful can draw water up over 30 feet. Same with fuel. Any restriction makes it 10X harder for the pump to do it's job.

 

 

Your tank has a drain. When the fuel level is down to a couple of gallons dump it out. This will remove most of the crap. Removing the tank is best though. Expect the mounting bolts to snap off if doing so.

 

Use a brass punch to loosen the hold down ring and remove the sender as it is delicate. Carefully clean the O ring seal and it can be reused. Rinse out with water for now. Gas fumes are extremely explosive!!! Now you can look down inside. The pick up tube is usually within a 1/2 inch of the bottom. Make sure it's not bent and sucking air when the tank is only 1/4 full.

 

I put several double hands full of clean gravel in my 710 tank and shook it and rolled it around. (for a long time) I've heard of using a piece of chain but this is sure to bend the pick up tube. Empty out and rinse out with a hose. I got all the gravel out but a few pieces won't hurt. Rinse thoroughly. If still rusty shit coming out do again. Let dry inside overnight or sit in sun. If really worried throw a half liter of menthol hydrate in and swish around and dump out.

 

Before mounting maybe blow air through the lines from the tank to the motor. Remove the fuel filter first and have something to catch it in. Install new filter and carry a spare. Mount tank and throw the other half liter of methyl hydrate in tank before adding gas. This will absorb any water. WallMart paint section Methyl Hydrate about $4 a liter or less.

 

In a week replace the filter. Cut the old one open an inspect.