I am still trying to get my "81 F-100 with a 300 I6, with 76,000 miles on it running properly. Starts and idles fine, but after a few miles boggs down, and chugs when I accelerate too hard. Also getting only about 10 mpg. I have to wind it up as high as I can before shifting because it will bogg at the lower rpms.

I have changed fuel filter twice, new plugs and wires, checked timing. I got truck from my Dad, and was not driven much in the last few years. Now with the warmer weather, I feel like looking under the hood again, before I bring it into a shop.


Thanks

Jim in MN

 

take the carb off, turn it upsidedown and see it the screws holding the carb body together have loosened up. they are well known for backing out.

 

what oldhaltons said, check the base of the carb for loose nuts, also check the screws that hold the carb together...I've had to tighten mine many of times...

 

Jimmn:

Yep...look at your carb like the other guys said. And while you're at it, take some carb cleaner and spray it on the outside of the carb while the engine is idleling. If it picks up some RPM's then you have found an area where the carb is sucking air. Tighten them screws up.

You didn't say if you have a clean air filter or not. Also look at the heat riser tube that goes to the snorkel on the air filter canister. If that door where the pre-heated air goes into is staying opened after the engine is warm, you will have some serious poor mileage and crappy pickup. That door or flap has to close after the engine is warmed up or else you will be drawing air from only that small door instead of the main ram air snorkel. You will be starving your engine for cold air. The heat sensors (light green and white colored) inside the air filter housing (where the air filter sits) go bad and so do the little vacuum hoses that run over and under it. They are what controls the heat door from opening and closing.

I took some golf T's and plugged my vacuum lines. This allowed me to keep the pre-heat door closed. It didn't affect my cold driveability. Hope this has helped you...and keep us posted on what you find. I have over 210,000 miles on my 81. It's never been rebuilt.

-hooD

 

I would also double check the timming. And then see that it advances when you rev the engine. No advance = no power...

 

Jim,does Your vehicle have a catalytic converter,if so it might be clogged up and causing a power loss.My 2 cents worth.
"bowties in the rearview mirror"

 

Like others have said, I would check the timing, when I advanced my timing the differnce was night and day, felt like a new truck!

 

Double post

 

check your timming. lol

actualy check for vacuume leaks and check the line between your Distrubutor and intake manifold. That has a vacume advance and without that line it will make it run like a chevy