adjusting the 1981 1bbl
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Senior User
Joined: Nov 2010
Posts: 146
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From: Air Capitol, KS
adjusting the 1981 1bbl
HI folks. I have a 1981 F100 with the I6 and stock 1bbl carb. I have determined that one problem I'm having is that my fuel mixture is running too rich. I think the fuel mixture screw is on the passenger side close to the front and on the bottom (though I'm not sure, just was reading some other threads). I need to ask if anyone knows if my thoughts are right on the proper mixture adjusting screw is correct and how to adjust this, whether in or out makes it leaner, and how should I gauge how much to adjust it. Also, are the idle speed screws on the driver side under the air cleaner? Finally, which bolt exactly loosens the distributor so I can adjust the timing (I'm embarassed to say I couldn't find it). Thank you for any tips and help (and pictures would be a spoda bonus). And wish me luck, because I'll attempt this adjustment in the morning so I can make it to my sister-in-law's graduation.
Elder User
Joined: Apr 2009
Posts: 922
Likes: 1
From: San Diego
because without better exhaust manifolds or headers, it doesn't give you all that much bang for the buck if any.
idle speed screw is on the lever that the throttle cable is attached to.
the one you spoke about should be the idle fuel mixture screw, it only adjusts fuel mixture at idle, in all other throttle positions the mixture is controlled by a metering rod inside the carb.
bolt for loosening the dizzy is at the base of the dizzy with a c shaped piece of metal that holds down on the dizzy keeping it where you want it.
Will see about photos, I am unbelievably tired at the moment... building a 10 x 10 shed out back, not as easy as I thought.
idle speed screw is on the lever that the throttle cable is attached to.
the one you spoke about should be the idle fuel mixture screw, it only adjusts fuel mixture at idle, in all other throttle positions the mixture is controlled by a metering rod inside the carb.
bolt for loosening the dizzy is at the base of the dizzy with a c shaped piece of metal that holds down on the dizzy keeping it where you want it.
Will see about photos, I am unbelievably tired at the moment... building a 10 x 10 shed out back, not as easy as I thought.
Senior User
Joined: May 2010
Posts: 350
Likes: 2
From: Spartanburg, SC
Sounds like its a stock setup and as 6fifty said, a four barrel is not an option without a few mods.
If you are standing on the driver side looking at the distributor, follow it to where it meets the block and the bolt is tucked at the base towards the front of the vehicle.
To adjust your idle mixture, run the screw all the way in, and back it out 1 and 1/2 turns. If it is still running too rich, run it in at half turn increments until you reach a good mixture. I have a Rally one barrel and from the factory it came with 1 and 1/2 turns out, but I had to go in 1/2 turn to get it right.
If you are standing on the driver side looking at the distributor, follow it to where it meets the block and the bolt is tucked at the base towards the front of the vehicle.
To adjust your idle mixture, run the screw all the way in, and back it out 1 and 1/2 turns. If it is still running too rich, run it in at half turn increments until you reach a good mixture. I have a Rally one barrel and from the factory it came with 1 and 1/2 turns out, but I had to go in 1/2 turn to get it right.
Post Fiend
Joined: Jul 2004
Posts: 8,786
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From: Northern California
The above is true except on Feedback carb systems. The first year of the Feedback carb was in 1981. So we need to know what carb he's got, either a regular carb, or feedback carb. Either were avaliable in 1981.
The feedback carbs mixture is controlled by the feedback solenoid, and the computer gets it's initial base setting from the idle mixture screw. If the idle mixture is out of adjustment it can throw off the computer and cause drivability issues in all driving modes. The adjustment proceedure is also more elaborate as the computer will fight you when you adjust the screw. So with every adjustment, you have to shut the engine off, and clear the computer then do it again, to get an accurate adjustment. Then keep adjusting untill you get a consistent mixture at idle.
