Signs of a weak mech. fuel pump?

My '75 Duster is driving me nuts. The Carter BBD 2-bbl carb had clogged idle tubes when I got it. Cleaned those out so now it idles well, but once you step on the gas and the initial accelerator pump gas shot is gone the car falls on its face. I noticed that the fuel pump is nice and shiny so I think it is new. One thing I noticed is that the plastic see-thru inline fuel filter never really fills with gas like my other carb'd cars do. My Oldsmobile's filter is full of gas except for a few tiny bubbles. The filter in the Duster has a thimble full of gas at the bottom and just a spurt of gas comes from the feed line at any one time.

I pulled the pump-to-tank line and blew compressed air through it so there are no blockages there. The fuel pump "looks" new but the car sat for two years. Is it possible that if the engine stopped while the pump was at full spring compression that the spring was weakened? I will probably just get another pump this week and swap it out. I just hate throwing parts at problem sometimes.

Is there a strainer in the tank that may be clogged?

Just make sure the fuel line between the pump and the tank is in good shape. Any holes and the pump might suck air, but fuel won't necessarily leak out. This happened to me on a VW Scirocco (pre-FI). Replaced the semi-rotten rubber hose before the pump and voila! Like magic!

carzan wrote: Just make sure the fuel line between the pump and the tank is in good shape. Any holes and the pump might suck air, but fuel won't necessarily leak out. This happened to me on a VW Scirocco (pre-FI). Replaced the semi-rotten rubber hose before the pump and voila! Like magic!

Yeah I'm dreading that one, but it is a possibility. The rubber hose between the hard line and the tank could be rotten and letting the pump suck air. Guess I should drop the tank anyway and make sure there isn't 35 years of muck in the bottom.

As far as anything before the pump, try a short length of hose into a gas can, and I recall that the mechanical pumps are usually rated for pressure & volume... just my 2 cents

Chebbie_SB wrote: As far as anything before the pump, try a short length of hose into a gas can, and I recall that the mechanical pumps are usually rated for pressure & volume... just my 2 cents

Now that is a smart idea. I might do that tonight. I've got a 1-gallon gas can and a length of fuel line already.

slefain wrote:

Chebbie_SB wrote: As far as anything before the pump, try a short length of hose into a gas can, and I recall that the mechanical pumps are usually rated for pressure & volume... just my 2 cents

Now that is a smart idea. I might do that tonight. I've got a 1-gallon gas can and a length of fuel line already.

Yeah, that's a great idea. If it still doesn't pump, make sure the pump lever is resting where it should be on the cam and the lever has free movement. Some pumps have to be shimmed in or out from the block for proper movement of the lever.

slefain wrote:

Chebbie_SB wrote: As far as anything before the pump, try a short length of hose into a gas can, and I recall that the mechanical pumps are usually rated for pressure & volume... just my 2 cents

Now that is a smart idea. I might do that tonight. I've got a 1-gallon gas can and a length of fuel line already.

mechanical pumps do not like to suck uphill and they can be damaged by trying to do so. make sure the gas can is about the same height as the outlet on the stock gas tank.

I'd go ahead and get the pump if it's cheap and then do the test. Compare old flow to new flow just to confirm to yourself that's the issue. Also remember to check the pump to carb line. I've seen them get dented or crimped on metal lines or swell almost closed on rubber lines.

I HATE mechanical feul pumps! I always switch in an electronic, wired to a hidden switch for theft deterance.

Another option is to give it throttle until it starts to choke, kill the ignition, and take the top off the carb and see how much fuel's in the bowl.

One goofy problem I had was big particles floating around in the fuel tank. Every once in a while, one would float over the inlet pipe and get sucked onto it. I'd coast to the side of the road, wait a few minutes, and then it would start like there was never a problem. Finally caught it by opening the tank access hatch and lifting out the little bastard clogger with one of those remote finger thingies.

Add a fuel pressure gauge after the pump.