I am new to this forum and need a little help. I have an '81 f150 with a 4.9l inline six with 82k orig. miles. 4x4/man. trans. Freshly rebuilt single barrel carb and head. New plugs, wires, cap, rotor, egr, pcv, fuel filter and some vaccum lines. I say some because all the lines that were there when I bought it I replaced. The rest are capped. The truck ran pretty good for awhile and then without warning started running like ****. The truck had been parked for 8 yrs. before I bought it. All parts except the carb. are new since I purchased it. I have checked the choke and even taken the carb apart to check the floats and everything still looks brand new on the inside. I replaced the coil with a used one that I had lying around that I new was good and no change. This problem also did not just appear after I installed the head. It came out of nowhere. It runs very rough at any rpm and will not idle. I have to hold my foot on the gas to keep it running and it is so bad that it shakes the whole truck and black smoke comes out the exhaust. I also tried removing the exhaust pipe and starting it to see if the converter was plugged, but no change. any help would be greatly appreciated. I'm pulling my hair out!!!! Thanks!

 

You took the carb apart to view the floats, but did you rebuild it? The rough idle and black smoke sounds like its running way to rich and points back to the carb. Pull some plugs on both side and see if you are fuel fouled. The carb can be sealed from sitting, so if it wasn't rebuilt, rebuild or replace it. Gaskets, floats and seals will all deteriorate over 8 years. You have either replaced or check everything else, so concentrate on fuel delivery.

 

Whoa Nelly, sorry inline 6 are in a row so disregard the pulling plugs from both sides.

 

Try tapping the carb top with a wrench when that is happening gotta be a stuck needle valve.

tom

 

Problem should be the accelerator pump in the carbureator. It is a very inexpensive part. I have had (2) installed in my old 79 F-150 since 1987. Symptons were exactly as you describe.

If accel. pump is not the problem: sucking vacuum somewhere around the intake (since you had the head off recently). I check for vacuum leaks (with the engine running) using WD40 in an aerosol can.

 

Stuck float needle...Rebuild the single lung(or is it the Holley two barrel) for 20 bucks. Carbs rule!!