I recently rebuilt a Motorcraft 2150 carburetor for a 1978 F150.

Put it on and tried to start it up, no go. Dumped gas down the carburetor, and it fired up then dies after using up gas dumped down it.

It's not getting gas to the bowl.

I took the hose out, crank the engine, and fuel flows out of the hose. So I have gas. Then I put the filter on the hose, and cranked it again. Fuel flowed through the filter. So there is no obstruction there.

Put the filter and hose back on the carb, and it won't fill the bowl. I removed the float, needle, and screen. All looks ok. I reinstalled them, and it still won't fill the bowl.

What gives?

 

If the float tang is bent at an extreme angle, the needle will seat even with the float sitting dry. You should be able to push the needle down into the seat while the opposite end of the float moves upward. Check that first. If that looks okay, try running it without the screen; it's not necessary.

 

The float tang was a bit bent outwards. I bent it back in in order to pull the needle up more. I can see the needle moving. The sheet calls for 31/64 for a dry float. But it still doesn't fill the bowl...there is a bit of gas coming out now. But not to fill it.

Then I made an assumption that the fuel pump must be weak if it can't pump that much upwards to fill the float. It was fine before because the bowl was always full. Does this sound correct?

 

I have occasionally had trouble with the needle getting slightly crossways in the seat and sticking. Put the old needle and seat back and see if the problem goes away, or if it changes to flooding (caused by leaky needle) If so, maybe new part is improperly machined. I have found the quality of parts from a famous foreign country to be variable. Could be your clip is wrong, or the float is damaged, if above doesn't help, buya new one. Borg Warner parts are more expensive, but still made in US, also last time I bought balkamp brand it was us made.

 

That could be a possibility. I saved the old parts. I'll try them out and see what happens.

Thanks for the insight.

 

No go.

I don't get this. This is frustrating. This is the first time I've had issues after rebuilding a carburetor.

No matter what I try to do, it won't fill up the forsaken bowl. I'm beginning to think I have a weak fuel pump. That's the only thing I can think of. I can't figure it out. Before the rebuild, it was running with the fuel pump flowing fine to keep the bowl full. Why the sudden change?

I took the whole assembly off - float, needle, needle seat, and the screen. It was down to the hole. Then I cranked the engine for 20 seconds. No fuel came out.

I gave up, and got some gas to fill the float. It caught and ran for a second then died down. Tried again, and it caught then died. Bowl is empty now.

I'm going to start over.

I know there is gas in the tank. I put 5 gallons in the tank two weeks ago. I didn't drive it, it should have sufficient fuel. But I will put another 5 gal in it later today anyway. There is a locking gas cap, so it hasn't been siphoned.

Replace the fuel filter. Maybe it's the wrong one.

Replace fuel hoses, although they look okay.

Replace fuel pump. The one on there is really old, and there's 5 or 6 fuel clamps sitting pretty on the output port.

Any ideas?

 

Let me get this straight - disconnecting the fuel line past the filter, right where it meets the carb, and cranking the engine - does put out gas? If that's the case, you can do a volumetric test. Let me know if adding more fuel doesn't fix it, and I'll look up the numbers.

 

That's correct. It did put out gas.

But when it is screwed into the carburetor, it's hard to get gas past the hole where the needle assembly screws into.

Is it possible the new fuel filter is choking down the fuel pump's ability to pump gas? Or it is too weak to push gas past a 90 degree elbow turn UP, defying gravity to flow down into the bowl?

The previous fuel filter was a Fram fuel filter that screws into the base. The current fuel filter is a Pruoplator(sp?) filter that also screws in the base. The Propulator one is much larger than the old one. I'll see if changing the fuel filter to an inline one does anything.

I have a glass bottle ready to be used for a volumetric test; can you please provide the numbers?

 

On the outlet side of the pump, you have a lot more freedom to route the fuel line because the pump pressure should overcome any upward movement the fuel must make as it passes through the pump-to-carburetor line. Check if any rubber hose is pinching off when the carburetor is hooked up.

Volumetric test: The pump should be able to produce 1 pint of fuel within 20 seconds. 20 seconds might be a little rough on the starter, so you might try half a pint in 10 seconds.

If you have a fuel pressure gauge, it should be about 5 psi. My vacuum gauge doubles as a fuel pressure gauge.

 

I have a short rubber hose. From the fuel pump to the distributor body, the fuel line is steel. The steel line was originally longer, but someone cut it for some reason. The steel line terminates upwards (vertically). A rubber fuel hose starts there, does an elbow bend, then it terminates at the fuel filter. The elbow is the only bend. From there it's a straight line to the fuel filter. It was in the same position prior to rebuilding the carburetor. It has reasonable slack. The rubber fuel hose is about 8-10 inches long.

I'll do the volumetric test.

Hey, that's right. Thanks for reminding me. My vacuum gauge does double as a fuel pressure gauge. I'll also test the pressure.

 

Did the volumetric test.

I only got about 1/2 cup of gas after I cranked for ten seconds twice. Cranked ten seconds, rest for 30 seconds, then cranked for another ten seconds.

The only conclusion I can lead is that I think the old needle was leaking like a sieve. Also, the float level was set extremely high. Maybe they made running possible. Corrected, the fuel pump showed its weakness.

Thoughts before I order a new fuel pump?

 

It looks like your fuel pump is only producing 25% of the specified volume. I agree with your reasoning to this point. Based on the observations you have thus far, it makes the most sense to try a new fuel pump. The good news is, mechanical fuel pumps are really cheap ($25 ballpark). Hopefully this fixes it. The volumetric numbers came from my Chilton's manual. Did you happen to try the pressure check?

The only other possibility I can think of is a fuel line leak.

 

That is what I am hoping as well. It is the only probable culprit.

I do not think there is a fuel leak. I haven't smelled any gas. The pavement where it's parked is dry. I do not have the evaporation emissions.

I did look at the fuel system when this issue first appeared. The hoses around the selector valve had been replaced recently (fresh rubber & shiny clamps). I have dual tanks, so tracking down which is steel and which is rubber just became more difficult. Especially when the auxiliary tank covers a large portion of the frame. But they appear to be leak-free.

 

I have seen the rubber line from the tank tot he frame dry rot and allow air to be sucked in and not leak fuel. Just an idea.

 

God, this has been crappy.

No go. New fuel pump. Tested it...now NO gas is coming out of the discharge hose. WTF!

I'm pretty sure I installed the arm under the eccentric cam. It went the same way as the old pump came out. I struggled getting the new pump in a bit. But then I haven't changed a mechanical fuel pump in ... yeah, that long! Suggestions?

Looks like I will just might as well rehaul the entire fuel system - cleaning/replacing tanks, new rubber hoses, etc etc. LxMan might be right, there may be air even though it's not leaking..not at least when stationary.