I want to ask this in its own thread because I am at a loss and do not know what to think at the moment. So I want to ask if anyone on here has ever seen what I will describe below or heard of it.


First off I rebuilt the Motorcraft 2100 carb as well as an AC stamped double action fuel pump.


When I initially filled the fuel tank up before it started leaking I cranked on the engine a little and when I looked the sediment bowl was full of fuel.


Now fast forward to yesterday when I got the engine running. The fuel bowl kept running empty resulting in the engine stalling out. I removed the short piece of rubber hose from the fuel pump inlet to the fuel line on the frame and took the old fuel hose I had and cut it up to get the barbed fitting to attach a hose. I threaded it into the inlet on the fuel pump and stuck a long piece of hose into a 5gallon can of gasoline same gasoline I had in the tank and removed when I saw the leak.


So I took and pulled the outlet hardline loose at the pump and cranked the engine over and fuel shot out under what appeared good pressure in large one two pulses while cranking so I know the pump is pumping. I figured the carb sitting with fuel in it must have caused the needle to stick closed. So I took the carb apart and nope everything was working fine. I removed the carb and even blew through the inlet while working the float and air flow was being shut off. So the carb is working fine as well as the fuel pump. But the thing is running out of fuel, you prime it by filling the bowl up and at a high idle after about 15 to 20 seconds the engine just loses power and stalls out.


I was told by my dad who was helping me yesterday that the fuel can sitting on the ground was too low. I told him the pump should still pick it up reguardless of how high or low the fuel source is. I even took the hose off and put my thumb over it while the engine was running and I didn't really feel a suction, also the hose I was using was regular vacuum hose as its all I had on hand and it did get a little soft but I don't think it was collapsing otherwise it wouldn't be spraying fuel out of the outlet when cranking.


I am at a loss on this and just putting this out there to see what people think till my fuel tank comes in and then I can try it out with the system hooked up as the factory intended it to be.

 

Howdy,

Glad you got that thing running!




Your fuel pump is a positive displacement pump, so it can easily "suction" the fuel out of the receptacle you're using.

Sounds like you may have a crack, leak some place in the supply hose allowing it to suck air.

Get yourself a piece of clear vinyl hose and put a heavy fitting on the suction end so it will stay submerged in the fuel.

Then crank the engine and ensure that you have no bubbles in the line.

You could also place a 0-15 psi gage on the discharge side of the pump to verify it's putting out the 5-7 psi a good pump should be able to provide.

Cheers,


Rick

 

Ok, I got my fuel tank in. I also did a pressure test on the fuel pump at the carburetor. Just cranking the engine over not actually running I hit and held 5 PSI. The specification in the shop manual sas 4 to 5 psi @ 500 RPM. I wasn't turning but 150 RPM at best and hitting 5 psi so the pump is fine pressure wise.

I took and removed the top of the carburetor and found that the gasket was contacting the float arm and thought it wasn't allowing the float to drop enough so I cut a window in the gasket. Same thing fuel bowl runs empty and doesn't pump up. I took and removed the top again and had someone watch the fuel bowl as I cranked on the engine and nothing. No fuel was entering the bowl. I took and removed the float and the needle seat and tried again and same thing no fuel entering the bowl.

I then took the hardline loose at the fuel pump and left it connected to the carburetor and blew through it. I can easily blow through the hardline and past the needle seat then when the float is lifted the air flow was cut off.

So as of now I am at loss because I have 5 PSI cranking the engine over which should meet the requirements of 4 to 5 psi @ 500 rpm. I didn't do a volume test but when I did have the hardline disconnected and cranked the engine over there was a good volume with each pulse and was under good pressure.

I am leaning towards carburetor but considering I already spent $70 on a rebuild kit and rebuilt this from the ground up and everything works as it should I have no idea what could be causing the fuel pump to put out and hold 5 psi of pressure but it not enter the carburetor even without the needle seat installed but yet you can blow air through it.

I am temped to purchase a reman carb but then that would be another $250 thrown away if I still have the same problem. I could also purchase a reman double action fuelpump then swap my lower section over to have a sediment bowl but then if that doesn't fix it then that's $200 thrown away there.


The only upside to this today is that I was running the engine and got it to run at a slow idle and next thing I noticed my gen light went out and the generator just all of a sudden started charging out of the blue so atleast I don't have to mess with the generator just need to resolve this lack of fuel to the carburetor.

 

If you have good pressure at the carb, that only leaves the carb as the problem......


I also would do a flow test though just to make sure you do get a good squirt of fuel...

 

I haven't had the time yet to do it after work due to weather and the fact it gets dark so early. What I plan on doing is taking the top of the carb off again, disconnect the hardline from the carb and attach a length of rubber hose with a funnel on the other end. In theory if I am thinking correctly on this me pouring fuel into the funnel should flow through the needle seat and fill the bowl up using gravity. If this does not happen then I have a restriction in the inlet of the carb. Not one that is preventing air flow but one that is enough to prevent fuel flow.


I will be checking that hopefully one day after work before the weekend since the rain should be out of here.

 

Left work early today to work on the car. Put fuel in a hose using gravity to the carb. It was pouring slowly into the fuel bowl. I then decided to take the carb apart a little to check it for blockage so I blew into the hose to get fuelout of the hose. Once I put fuel in the hose I could not blow through as hard as I tried nothing. So I took the needle seat housing loose and checked the mesh filter it was clear. I the blew trough the hose and out of the carb inlet in the bowl came some dark pieces.


I realized what happened now. When I had the fuel pump and carb apart and rebuilt it, I did not take the metal hardline and flush it out between the pump and the carb. So any junk in the hardline from the tank to the fuel pump will be stopped by the brass mesh strainer in the sediment bowl, any junk in the hardline after the fuel pump just got pumped into the carb mesh and caused my problem.


Now I need to look at getting the radiator recored or purchasea new one. Before then I need to check the dwell, and the RPM and set the carb, the engine idles fine but its a little rough. The exhaust also has a slight rich smell so I need to play with the idle mixture as well.

 

Outstanding, glad you found the problem. One thing I re-read some of your troubleshooting steps. You did make one assumption that is reasonable, but COULD cause a problem, technically. Since the fuel pump provided 5 psi @150 cranking RPM, it "should" be OK, but fuel pumps CAN be defective on the high side, too. Not saying this will be a problem though check to be sure when you get a chance.

 

I will be, I will be installing a Tee to allow the engine to run as well as read fuel pressure.


I read vacuum on my fuel pump and the vacuum was fluctuating between 5 and 10 inches and spec is min of 10 in at 500 rpm. Not sure what rpm I am turning at full idle I need to check that when I go through the carb adjustments from the choke, to idle mixture, to fast idle speed and slow idle speeds.

 

It's usually something simple!!