I'm new here, so please go easy on me. I have an '81 F150 with a 300" six and a four speed stick. It's bone stock and has ~168 thou. on it. The truck has always been reliable transportation and I've only put about 4 or 5 thousand miles on it a year. I've been real good on the maintenance and don't use the truck for much other than transportation on the freeway to a near by city.

Lately though, the truck has been suffering from poor mileage (10-12 mpg mixed, but Oregon puts booze in their gas) and even more recently, has been having performance issues. It will stutter slightly when starting out from a red light. If I get the truck on the freeway, it has a real hard time getting up to 65 mph and once there, seems to have no power. Strangely enough though, the truck still runs good enough (despite the stuttering when starting out) to get around in town at slower speeds.

• I put in a new fuel pump, but that wasn't the problem.
• I pulled the carb (YFA non-feedback, E1TE-DA) and promptly lost the pump check weight, so I carefully fabricated a new one (they're supposed to be .304" long and .140" wide, square in cross-section but I made mine round.) Then I *very* carefully rebuilt the carb. The symptoms remained unchanged. I've gotten so good at taking off that carb, I can do it in about five minutes now.
• I've set the idle mixture screw, float and metering rod *very* carefully to the correct specs.
• I've verified that the distributor advance mechanism is still working correctly and have checked the timing, which is dead on.
• I've checked my plug wires and plugs. They're all good.
• I've checked my air filter and although it's used, it only has a couple of thousand miles on it and is still serviceable (I can see through it when held up to the light.)
• My fuel filter is like new and is clear.
• I have no fuel line leaks.
• My gas tanks (there are two) have no gunk in them. I blew compressed air through the fuel lines after disconnecting the line from the fuel pump (with gas caps *off* to avoid pressurizing the tanks and blowing up the truck!)
• There are no leaks in any of the vacuum lines and they are all correctly attached.
• The EGR valve is new and has no problems.
• My belts are all good and my thermactor air pump is working correctly.
• My exhaust system is in good shape and my heat riser isn't stuck, is opening correctly.

I tried to make the above list as complete as I can, but I'm an old dude and may have forgotten something I tried, so please cut me some slack. I'll definitely let you know if I tried something which you suggest.

I am at my wit's end with this problem. Add to this that I get to work on the thing in the street in front of my house because I don't have a driveway or garage, that the truck is parked facing uphill so that everything I drop rolls away to someplace downtown, and you can see that it's not a lot of fun to deal with.

Does anybody have any other ideas what it might be? Thanks in advance for any help and suggestions!

Regards,
Floggit

 

Welcome to the forum, Floggit!

A very thorough list... you did not mention the distributor cap or rotor. Have you checked them? What about the catalytic converter? A compression test will tell you if the engine has a weak cylinder or more. What about the choke? Is it opening properly?

 

When it's sitting in the driveway, fully warmed up and idling, does it hesitate when you smash the gas to the floor for a second?

 

Thanks for replying!

Sorry, I knew I forgot something. The distributor cap and rotor are fine. The catalytic converter is... well, it's there. I don't know how to check it. If it's messed up, I can't afford a new one and would probably just remove it.

The choke has always been disabled. The original owner turned it all the way over to lean and I like it that way anyway (I've owned this truck since around 1995 or so.) I verified that the choke valve is all the way open too.

Regards,
Floggit

 

Thanks for replying!

I don't have a driveway, unfortunately. Remember, I have to work on this thing where it's parked in front of my house. But yes, when it's fully warmed up and idling (which it does nicely), there is a very slight hesitation when I mash the pedal to the floor for a second. And by the way, it starts right up when it's cold too.

Regards,
Floggit

 

Take the aircleaner off, and get a flashlight. Climb up in the engine compartment, and shine the flashlight down the throat of the carb(engine is off). While looking down the carb throat, push the throttle back. The very slightest movement should start the accel pump squirting fuel. If you have any delay in the fuel stream, or your fuel stream is not very strong, you still have problems with your carb. Your accel pump needs to inject a good bit of fuel AS SOON as the throttle is opened, to cover up and prevent the engine from going lean.

 

I was also going to recommend the catalytic converter. My neighbor just a couple of weeks ago had very similar symptoms. After driiving it...the exhaust manifold and converter were glowing red it was so hot. His was completely plugged....possibly your's is starting to plug?

 

I had this problem also with my 84 302 where id replace the fuel filter and 5 miles later it would plug up again. After about 5 times replacing it and cleaning everything it solved the problem. Its a cheap and simple fix and might be worth a try.

 

Well, I found out what the problem(s) were. Turns out I had a broken spark plug from overtorqueing it. Also, had a bad distributor stator. One problem is usually easy to find, but two at the same time makes it far more difficult. Regardless, the truck is running fine now. Hope it stays fixed for a while this time. Thanks to everybody who replied!

Regards,
Floggit