Fuel pump

[gick70]

When does a mechanical pump go bad?I could see air bubbles in my gas filter before carb every now and then,and it seems it starves for fuel.The pump looks pretty new,but it could have been sitting a few years,dry rot in diaphragm?

 

[Broncobowsher]

They usually die when they start leaking fuel (externally onto the ground or internally into the engine oil). The check valves can go bad as well. Few other things.
The air bubbles could be a lot of things, none that I can blame on a fuel pump. Depends on what the bubbles are. Boiled fuel (early stages of vapor lock). Sloshing fuel in the tank allowing bubbles, gulps of air, into the pickup tube. Completely normal for carbureted engines. That is why there are fuel bowls in the carburetor, to take care of this stuff and get back to a steady reserve of fuel at the point of use. Also selector valve leaks, minor leaks on rubber hose or even porous rubber hose. Air leaks in through holes a lot smaller than fuel can leak out of.

Occosional bubbles are not a concern of mine.

Now the starved of fuel, when does this happen? First thought there is fuel filter.

 

[dave67fd]

I would check your fuel line feed first for any dry rot. Fuel line could actually have a pin hole (and not leak) and can introduce air into the system. You could put a short line of new test line from the pump input into a portable fuel tank and see how well it pumps. May take a few seconds to reprime. Just stay safe doing so.

 

[blubuckaroo]

A leaking selector valve can leak air in, causing loss of prime at the pump.

 

[bronconut73]

A leaking selector valve can leak air in, causing loss of prime at the pump.

This/\/\/\/\

Even if it ain't technically leaking fuel out, it can still suck air in.

 

[gick70]

No tank selector,also I was thinking maybe some vapor lock,how do you run lines off the fuel pump staying away from the heat?351w carb?

 

[gick70]

Anybody?

 

[ntsqd]

On the Ranchero's 302 I just came up the front of the engine avoiding any confined spaces where there would be little to no airflow.

On the Bronco (351W) I went with an electric pump at the tank, jumped off the frame above the clutch linkage, and came up over the bell-housing. Not much help there.

Starving for fuel could be a whole range of things. Old fuel hose will get burst aneurisms that turn into flaps that partly or fully block the hose. Rust or other junk in the fuel tank can block the pick-up or plug the lines. Could be vapor lock too.

Start with the fuel tank, make sure that it's clean. Then, how old are the fuel hoses? This stuff we buy called fuel is really aggressive towards the older hose formulation. I'd say if the hoses are more than 5 years old or are the cheap stuff then it should be replaced. I'll suggest that, though expensive, that "Emissions Barrier Hose" will save you from going thru this again.While you've got the hoses off check for flow of the lines.

 

[jckkys]

My 351 is set up just like the original 302. The fuel line to the engine lies on the frame with a rubber hose to the pump. A steel fuel line goes from the pump to a filter at the carburetor. I tried several clear filters and found that air bubbles are irrelevant. They aren't related to fuel starvation. They aren't a good choice for a filter either because a crack can cause an engine fire.
If the output of the pump at is proven adequate by the test that dave67 describes I would look at the carburetor. I know the 2100-2150s had a screen under the needle and seat when new. Other carbs had similar "last chance" internal filters or screens. So the blockage could be inside the carb. Squirting some carb cleaner in the inlet to see if it comes out at the needle and seat assembly, will tell you if it's clear.