I have an 81 F100 with a single barrel carburetor, inline 6, 3 speed manual transmission. I have noticed that the engine was idling really high so I got in the engine to turn the idle screw and noticed that the whole carb was loose, really loose. After I tightened it down I turned down the idle a little and ran it. It sounded fine so I shut up everything and went to work the next day and the truck died on me about 7 or 8 times, whenever I came to a stop. Thinking it was just my idle too low I turned it back to where it was originally, started it up and went to look at it and gas was gushing from my fuel line that enters the carb. I clamped the line, no leaks, tight carb, and the idle screw set at the original spot. My truck still died almost every time I stopped on my way home. I am not sure what the problem is at this point but it feels as though it's running out of gas (there's still half a tank).

 

Maybe time for a rebuild? The idle RPM isn't going to change on its own, something else caused that. Maybe a vacuum leak - loose carb flange would do that.

 

grab the top of thr carb and see if there is any movement.from experience the base and top are famous for separating try tightening them

 

bert cook those were the ones that were loose when i had tightened the carb. Tedster9 if there was a vacuum leak why would it run better when the carb was loose?

 

Well - "better" than what? There's more than one thing going on here at a guess. Oftentimes we can fix or discover other problems by simply performing routine maintenance. It's pretty safe to say a carb of that vintage needs a good going through, cleaning, adjustment, new gaskets, float inspection/level etc. Then torque everything down evenly and see what you got. Jus' Sayin' what I'd do, without being able to look at it. Got any pics?

 

Well when it was loose it ran better as in it never died or chugged like it was out of gas. The rebuild was the next thing i was going to do, it wouldn't surprise me if it were clogged with silt too. The truck was my Uncles so there's no telling what he had done to it to make it run but he did take good care of it. I will try and get some pictures

 

hayes2go,


Quite possibly the carburetor halves have been loose for some time and the idle fuel mixture had been adjusted to compensate for a lean condition. When you tightened the carburetor screws, that lean condition was corrected, so now the idle mixture is rich.


You mentioned adjusting the idle speed, but not the idle mixture [different screw].


The gushing fuel line was a coincidence since the fuel line was removed so the carburetor could be turned upside down to tighten the screws. Glad you caught it before a fire started [hot exhaust, just below].


Find the idle mixture screw [base of carburetor] and gently turn in until it bottoms out. Then, back it out 1 1/2 turns. This is a good starting point. Start the engine and allow to come to operating temperature. Then, while idling, adjust the idle mixture screw in or out until you reach the highest RPMs or engine vacuum, if you have a vacuum gauge. Once you find the "sweet" spot, you will need to reset the idle speed screw.


When you removed the carburetor, did you replace the base gaskets? There should be two [1 beneath the EGR adapter and 1, above]. If these are old or damaged, a vacuum leak will occur. Make sure the two nuts which hold the carburetor down are snug.


Did you reattach the vacuum hoses which attach to the carburetor?

 

1986F150six I was thinking something similar about it having been like that for a while, but I have not adjusted the idle mixture. My next step was going to be replacing gaskets and cleaning out the carb, but I will try the other screw first. I made sure I had everything hooked back up before running it. Thanks for the pointers

 

That was the problem! Thanks everyone for their help

 

You should rep David/1986F150six for helping you. Click the scales icon at the top right of his post to add to his reputation.

 

so it was the idle mixture then? Thanks

 

From reading all the posts that is what I came away with.

Because the carb came loose a little at a time and started running poorly the idle mixture was adjusted.
Now that he loose carb was fixed but the mixture not put back where it needed to be it would not idle right.
Dave ----