Fuel Not Making It To The Carb!

[Vvajk]

HELP!

Here's the situation. I have the stock I6 AMC 258 i6 / 4.2l engine but with a Motorcraft 2100 carb, with manual choke. Right now, the only way to get the Jeep started is to actually pour gas from a can into the carb. After I do that, it fires right up and runs great, but it will not start by just turning the ignition. So I'm thinking, obviously fuel is not reaching the carb.

I pulled the fuel line off the carb, and turned the ignition, and fuel DID start to flow from out of the end! What the heck, right? Well, I'm sitting here at work, and it just occurred to me that I also have an inline electric fuel pump that is manually activated with a switch from inside the Jeep. When I flip the switch, the pump definitely kicks on (makes noise) but Maybe it's not pumping? What do you guys think, could this be my problem even though cranking the engine over still seems to be pushing fuel through the line? Maybe the inline pump isn't working, and without its help, there isn't enough pressure to deliver fuel to the carb?
I'm pretty amateurish about this stuff, I would love to hear from some of you guys what you think?

 

[Torxhead]

Setting up an externally mounted fuel pump can be kinda tricky, since electric pumps do not suck as well as pump. So the fuel has to be siphoned into the pump, this can require the pump to be mounted at or below the bottom of the tank, or very close to the fuel tank. The fuel tank must also be well vented. Also if you have the 3 hole fuel filter, the return outlet must be mounted at the 12 o'clock position. Cracked fuel inlet lines are also known to create problems. So if you are set up correctly it should work or you could have a burnt up pump. I would first recommend reinstalling the mechanical pump or checking the fuel pressure visually or with a gauge. If everything is good there, you might have an issue with the needle and seat assembly.

 

[Lumpy Grits]

Go back to the OEM mechanical pump.
There is no need for ele. fuel pump on a carb'd AMC 258 i6 / 4.2l .
Is the ele pump real close to the gas tank?
LG

 

[Geep]

Question : If a mechanical fuel pump was installed incorrectly, in other words the pump arm not making contact with the eccentric of the cam , would it even pump gas at all and would the arm be damaged when the engine was turned over ?

 

[Vvajk]

Go back to the OEM mechanical pump.
There is no need for ele. fuel pump on a carb'd AMC 258 i6 / 4.2l .
Is the ele pump real close to the gas tank?
LG

I'm a little dumb on this, but I've always assumed that the mechanical pump is still in there somewhere because fuel still moves through the line with or without the electric inline pump. Or will the engine compression do that too? I've always thought that whoever installed the electric pump did it as means of assisting the fuel to the carb. There are also two fuel filters on either side of the electric pump. I'm going to have to monkey around with it this weekend and see if I can chase down the possible problems. OR .... GASP .... take it somewhere and have a pro look at it.

 

[82Laredo]

It doesn't sound to me like a fuel supply issue but rather a carb problem. If it cranks and runs fine after pouring gas down the carb then it's getting fuel or else it would sputter out quickly. The float bowl in the carb should hold enough gas for it to restart and idle for a minute even without the fuel line connected. A couple questions for you...

Do you have to pour gas in the carb for every restart after it's been running or just when sitting for a day or longer?

When trying to start it are you pumping the gas pedal or just pulling the choke?

Have you taken the air cleaner off and looked down the barrels while moving the linkage to full throttle and seeing if it sprays fuel? (With the engine off of course)

 

[Torxhead]

I'm a little dumb on this, but I've always assumed that the mechanical pump is still in there somewhere because fuel still moves through the line with or without the electric inline pump. Or will the engine compression do that too? I've always thought that whoever installed the electric pump did it as means of assisting the fuel to the carb. There are also two fuel filters on either side of the electric pump. I'm going to have to monkey around with it this weekend and see if I can chase down the possible problems. OR .... GASP .... take it somewhere and have a pro look at it.

It is not uncommon to install an additional pump, but if the electric version did fail it would prevent fuel from getting to the next pump. Installing two fuel filters in this case doesn't make much sense to me. You could just follow the fuel line back to the gas tank to see just what all is there.
Edit: Oh yeah, one filter should be mounted prior to the pump as to protect it from whatever gets past the fuel tank pickup sock. The filter should be a high flow type for low resistance to the pump. There should be a oil pressure controlled switch so if you tip it over or get into an accident the fuel will not keep flowing. With a carb engine, it is so much easier to use one mechanical pump to avoid all the hassle of external mounted electric pump complications.

 

[Lumpy Grits]

I'm a little dumb on this, but I've always assumed that the mechanical pump is still in there somewhere because fuel still moves through the line with or without the electric inline pump. Or will the engine compression do that too? I've always thought that whoever installed the electric pump did it as means of assisting the fuel to the carb. There are also two fuel filters on either side of the electric pump. I'm going to have to monkey around with it this weekend and see if I can chase down the possible problems. OR .... GASP .... take it somewhere and have a pro look at it.

Very good chance that IF the ele pump has failed, that the ele. pump is restricting the fuel flow for the OEM pump.
Can you see if the OEM pump is mounted and the lines run'n to and from it?
When was the last time you changed the fuel filter?
Buy a FSM(factory shop manual)and learn to do it yourownself.
LG

 

[Vvajk]

It doesn't sound to me like a fuel supply issue but rather a carb problem. If it cranks and runs fine after pouring gas down the carb then it's getting fuel or else it would sputter out quickly. The float bowl in the carb should hold enough gas for it to restart and idle for a minute even without the fuel line connected. A couple questions for you...

Do you have to pour gas in the carb for every restart after it's been running or just when sitting for a day or longer?

When trying to start it are you pumping the gas pedal or just pulling the choke?

Have you taken the air cleaner off and looked down the barrels while moving the linkage to full throttle and seeing if it sprays fuel? (With the engine off of course)

I can shut the engine off for a while and it will restart, but if I leave it for a day or more then I will have to get out the gas can and pour gas into the carb for it to start. I do pump the pedal a few times (always have) before starting.

Just now, I took the whole top of the carb off, and there was still gas in the chamber, where the float is, from several days ago. I wiggled the float around, and moved the throttle lever a few times and heard it making a sucking sound. I put everything back together, and tried again, and BAM! she started right up! I wonder if the float was sticking or something?

I took it for a drive around the block, but only made it about half way when it started running really sketchy, like acting like it was going to die if I didn't give it a lot of gas. I limped back to my driveway where it died. I waited a few minutes and tried starting again, and she fired up like it was nothing. I let it idle for a couple of minutes and revved it a few times. It seemed ok, but I didn't take it for another drive. It sat all winter and a lot of the Fall ... I wonder if the 1/4 tank of gas is old and that's why it was giving me fits. I don't know. I'll try a cold start sometime tomorrow and see if it starts. That will be the true test.

 

[Lumpy Grits]

Run a temporary rubber fuel line that bypasses/eliminates the ele fuel pump.
Disconnect the electric to the fuel pump also.
Now, do a road test.
LG

 

[Geep]

I had a similar problem. AMC 304 V8, 2bbl carb and mechanical fuel pump. Start it up , no problem. Let it warm up, take it out for a ride and 1/2 mile down the road it acted exactly like it ran out of gas. tried to re start, nothing. took the air filter off and looked into the carb. manually worked the throttle linkage and gas was squirting into the carb , started it up ran another 1/2 mile or so and the same thing, like it ran out of gas. When I finally got him back home I thought it was the fuel pump not working up to capacity so I went and got a new one and installed it, same problem ! Installed a clear fuel filter between the pump and the carb replacing the solid one, so I could actually see how much fuel was being pumped. Started him up and watched the filter at idle and half throttle. It was barely squirting enough gas to keep it going. next thing, I pulled the fuel line from the pump that goes back to the tank, removed the gas cap and gave it a shot of air into the fuel line to the tank. That seems to have solved that problem but......you think I blew the sock off the fuel inlet ?

 

[Torxhead]

Geep as I recall, those socks do slip on, making it possible to blow off the sock if it was clogged up or it could have just cleaned that sock out. Inspecting it would be the only way to make sure. Anyway not having a pick up sock would allow junk from the fuel tank into the fuel pump. Installing one of those see thru fuel filters prior to the fuel pump might help here.

 

[Vvajk]

So I just went to try to start it after letting it sit overnight. It didn't want to start, but eventually I was able to get it to start after pumping the pedal ... A LOT. I took off the air cleaner and looked down into the carb while manipulating the throttle linkage. I could see these two little jets were squirting gas into this little round reservoir when I did. Finally after doing this a lot, it did start.

 

[defibvt]

Have you torn apart the carb and cleaned it?

 

[82Laredo]

Have you torn apart the carb and cleaned it?

I'm also leaning towards a carb cleaning since I'm guessing the problem stared after sitting for the winter.

It also wouldn't be a bad idea to drop the tank and inspect the pickup tube and filter sock. I was chasing fuel issues and found this:

View attachment 19204

No filter sock and partially clogged pickup. Also went ahead and unhooked the fuel line from the pump and blew compressed air through it for good measure.

 

[82Laredo]

Run a temporary rubber fuel line that bypasses/eliminates the ele fuel pump.

Disconnect the electric to the fuel pump also.

Now, do a road test.

LG

^^ and this seems like a quick and easy way to rule out the electric pump. Start here!

 

[jammer1]

^^ and this seems like a quick and easy way to rule out the electric pump. Start here!

Run it from a fuel can with new fuel would also help (in case of bad fuel, fuel just doesn't hold up as well as it use to).