Moved tank, now it runs bad

[Hudsonaj36]

I moved my fuel tank to the rear, put in a new mechanical fuel pump, and a new steel fuel line. Now it's running lean??? Tried another new fuel pump and no change. Tried new filter with no change. Any ideas?

Not using a return line and I do have the tank vented.

[Mmorgan32]

Put in an in tank pump to push the fuel. I don't think a mechanical pump on the engine will work with your tank that far away maybe a pump with more psi?

[Already Gone]

I have an ECE stainless tank that I want to install in my 72 stock 350 engine longbox. I was talking with my insatller yesterday and asked if my mechanical pump on the engine block would be sufficient to suck the gas from the back of the truck and he said he has done a few of these and the stock fuel pump on the block has done the job. I'll be watching this thread for other comments, ideas.

[Hudsonaj36]

Yeah I figured a lot of cars came with rear mounted tanks and the pump is a carter street and strip 6psi at 110gph. The tank is poly with a sump and the line comes out 90's up about 8 inches then 90's over about 8 inches then follows the frame to the pump.

[Hudsonaj36]

I almost feel like it's a coincidence and I just happens to get a vacuum leak at the same time, but there were no issues prior to moving the tank.

[Mmorgan32]

Maybe something obstructing the opening at one of your fittings? Like Teflon tape

[Mmorgan32]

If the vacuum leak is on your carb that will make it run lean

[cdowns]

The good old mechanical pump worked just fine for the millions of suburbans on the roads for the past 50years or so


makes you think

[Already Gone]

Originally Posted by cdowns

The good old mechanical pump worked just fine for the millions of suburbans on the roads for the past 50years or so


makes you think

Excellent point..

[Hudsonaj36]

I'm going to run it out of a fuel can next to the pump and see if that changes anything.

[cdowns]

Originally Posted by Hudsonaj36

I'm going to run it out of a fuel can next to the pump and see if that changes anything.

SURE IT WILL PROBALY RUN LIKE A TOP DUE TO PROPER VENTING OF THE fuel can

makes you think

[Hudsonaj36]

The tank is also vented, I even removed the cap to verify but no change

[70']

What process was used to ensure all the air was purged from the new fuel line? I would suspect an air bubble in the line between the tank and the pump. Probably in a bend, which would allow flow, but maybe not full flow to adequate feed the pump. If it were me, I would unhook from the pump, and purge the line with fuel backwards to the tank using a small hand pump, then reconnect and see what happens.

[Hudsonaj36]

I sucked fuel through with a hand pump, even though a mech fuel pump is self priming

[MARKDTN]

Where is the filter? It may not work if you try to suck through a filter. The filter should be between the pump and the carb.

[Hudsonaj36]

The filter is between the pump and carb

[Redline novdog]

can you put a pressure gauge on by the carb? Just jacking up a vehicle can slosh sediment from carb bowl into the jets.Filters don't catch everything !

[autocross]

What size fuel line did you install when you relocated the tank. It should be at least a 3/8 ID line if its got more HP then stock. A return line is good to eliminate vapor lock. It could also be something in one of your jets blocking fuel too. Pull the fuel line from the carb. have someone crank the motor over while you catch it in a measuring cup and see if your getting it there. If you are then it's filter or in the carb itself.

[brad_man_72]

Put the original fuel pump back on. You may be pushing fuel past the float valve. Worth a shot for free.

[clemsonteg]

Have you checked all connections? A loose connection could cause the pump to suck air rather than fuel. Not enough fuel=running like crap. I had this issue yesterday when driving down the highway. When I got home I found a hose clamp on my pre pump filter had come loose. It didn't allow fuel to leak out, but it allowed the pump to suck air and not deliver enough fuel when the engine was under heavy load.

[Hudsonaj36]

I'm going to do some work on it tomorrow

[cplcorndog]

Hi there,

So a lot of good information from the reply's, so I'll give you what I did and no issues since. I added an electric switched Holly pump. My guess is that your tank is to far away to get the proper amount of fuel, and your mechanical pump is most likely trying to suck fuel though a filter, almost like a straw. Even if you got it to work correctly, I'm certain that you'll over work your pump and burn it up.

If you get an electric pump place it as close to the tank as possible and then place a filter between the electric pump and carb (like said earlier). Electric pumps are made to push fuel not pull it. Then place your regulator somewhere in the engine bay so it's easy to adjust the psi on it. If you don't have a psi valve, you should get one. I hope this helps in some way.

[racerface]

Cdowns hit it right on the head. The mechanical pump will work fine. Electrical pump just covers up the problem. Use 3/8's line and double check the system from tank to carb. Happy hunting.

[SierraMtns]

Do you still have the in cab tank installed? You could switch it back and see if it fixes the problem.