Hello all,
I have recently been having issues with my truck. It is an '80 F100 with a 302 and a C6 transmission. Here recently my truck will run at idle and then when I drive it, the transmission will cycle through the gears, first- second- third, however I am having an issue with the speed. I cannot get her to go past 50 mph without her starting to chug and then losing power. When she loses power, she also loses speed. When all this happens I attempt to, so-called, mash down on it to see if it is a lack of fuel issue and it just slows down and it sounds like it is running on 2 cylinders. I need help please. This is my only way of getting back and forth to work til my other truck gets running.

 

Sounds to me like you might be having carb problems (accelerator pump possibly). Whens the last time the carb was rebuilt?

 

I had a problem similar to this once, the cause was a too-restrictive in-tank filter which wouldn't let through the required amount of flow for anything more than approximately 2,800 RPMs

 

I agree, it sounds like it's starved for fuel.

 

I have recently rebuilt the carb. By recently I mean about a month ago. I would a vaccum line to the fuel tank be causing this? Mainly because I have noticed the fuel gauge has been slow to read once it hits 3/4. Ctubutis, what do you mean by in tank filter? I think mine has one, not sure, but could it be dirty and creating the same issue?

 

The sending unit in the tank has a sock on the fuel pickup to keep large debris out of the fuel system.

Even though you recently rebuilt the carb, I would check your fuel filter again(the one at the carb). If you have a rusty tank, it can quickly clog again. You can take it out and shake it and see how much stuff comes out.

 

I had tried to use a rear tank sending unit that had an electric pump on it with my 1981 non-EFI truck.

The original filter on the sending unit had disintegrated so I tried to substitute, um, quite seriously, a white athletic sock.

It seemed like it would have worked, and I fastened it to the pump assembly with plastic ZIP ties.

The factory filter/screen/sock assembly looked similar to this:


Probably the combination of the sock + the unused-but-installed electric pump created too much restriction and the engine would sputter and die at around 3,000 RPM, flipping the switch to the other tank immediately cured the problem.

A stock 1980 302 doesn't have any electric fuel pumps, everything is mechanical. So, I would probably check fuel pressure and output flow rate at the carb's connection and go from there. IOW disconnect the fuel inlet from the carb and install a pressure gauge on the line, pressure should be I believe 4-7 PSI.

You can also check output flow rate, direct the output into a glass jar or bottle or something and see if it looks like it "should be enough."

I'm going to guess that your slow-to-read gas gauge problem is caused by the sending unit having worn out. Disconnect the wire from the sending unit and ground it to the body or frame with the key in ACC or RUN, the gauge should swing to FULL. Un-ground it and it should swing to EMPTY.

If that test works, that means the gauge & wiring are most likely OK and the problem most likely exists in the tank sending unit.

That won't have anything to do with your engine's running problems, though.

 

Franklin2: I rebuilt the carb and it has one of these on it, Amazon.com: Seachoice #20941 Univ InLine Fuel Filter: Sports & Outdoors. I can see through it and when it is running, the fuel fills it sometimes and sometimes it just runs though it.
ctubutis: I will try the grounding of the wire for the gauge, then if I have the chance,will drop the tank and see if the filter/ sock is gone.

 

That filter should get the majority of the crud. But, I'm not sure it'll get the silt that I'm getting from my tank, and I know from experience the silt will clog passage in the carb. My accelerator pump quit quickly after a rebuild because the silt had plugged the discharge orifaces.

I'm now using the cheap plastic see through filters that have a pleated paper filter element. They get all the silt and the carb is staying very clean. In fact, I run one ahead of the mechanical pimp and one after, and have to change the first one frequently.

 

Yeah my dad did that with his 83, the double filter, and he said it works great. However his truck is currently down due to some front end issues.

 

From 302 Carb Help forum:
"A quick question, If the ball and tube where the venturi attaches were not replaced, would that cause the carb to have problems."
Would this cause the problem I am having with the fuel and carb?
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One other issue that can cause this problem is restricted exhaust, collapsed pipe (most are double wall and the inner will "buckle"), bad catalytic converter. In you can get a fuel pressure gauge on it you can see if it is indeed starving for gas. One carburetor item, on the float at the needle and seat end, there is a clip on the needle that hooks over the float tang. If it is missing, the fuel pump can't develop enough pressure to raise it high enough fro full flow. You may have fuel pressure, but still be drawing the level in the bowl down. On the ball and tube, I assume you mean the accelerator pump check ball and weight, or the hollow screw itself?

 

I think I have officially fixed it, I opened up the carb and found out the ball for the venturi was completely missing. I took it for a test drive and she is running wonderfully. Im hoping I dont have any other issues with her. I am going to pull this engine out and put in a 302 HO so I can do all the much needed work on this engine.