rough idle and missing
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Freshman User
Joined: Jun 2010
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rough idle and missing
my dad has a 86 f150 with a straight six and we cant seem to get it to run like it should it misses and shakes pretty good at idle but seems to have plenty of power and runs a little better once you get going any help would be appreciated been tryin for weeks to get it to run better he is only gettin about 10 mpg
New User
Joined: Apr 2010
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I don't know much but thats how my 85 was too until I bought a new (not rebuilt) Rally YF (not feedback) carburetor. Its for an earlier pickup (if I remember right its identical to Holleys 1126 carb model) Someone on this site pointed it out to me on ebay for $160 TYD. To go with the new carb you need a vacuum advance distributor $70 or $80 and "blue graumett"duraspark 2 ignition modual $25. Then if you can find a wiring harness at a junk yard or somewhere and take the "can style" coil with the harness. Its so easy, plugs right in, and for about 300 bucks my pick up is running like a scalded dog, smother than it ever has since I've owned it and getting about 14 mpg pulling a 20 ft cargo trailer, I'm guessing 16-17 empty highway!! I love it.
Cargo Master
Joined: Apr 2010
Posts: 2,936
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From: Acworth, GA
A good starting point would be to check all of the vacuum lines and caps. On my 85 F150 (4.9L), they seem to wear out and deteriorate reasonably quickly. A vacuum leak can lead to a rough idle and poor gas mileage.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Agreeing with Grubbworm, also check that the two bolts which mount the carburetor are snug. They tend to loosen due to vibration and a vacuum leak is the result. Take the air cleaner off and grab the top of the carburetor and try to wiggle it. If it moves, it is loose.
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Freshman User
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if i rember right the motor is out of a 81 ford f150 and he is running the 86 carb we tried unhooking vac lines one at a time and made no differance actually the only vac line that is hooked up is for power brake booster it runs just as good with all lines off as it dose with them all hooked up we have looked for holes in lines 2 times and can not find one tried spraying starting fluid around base of carb and vac lines and the only placed we sprayed it that made a differance was in top of carb also it runs better with spout conn unplugged base timing is set at 10d btdc
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Cargo Master
Joined: Dec 2004
Posts: 3,362
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From: Florence, SC
Without proper punctuation and separating your sentences, it is very difficult to read your post, broncoman72. Try proof reading what you write before you submit your questions in the future. You will probably get more responses.
Therein probably lies your problem. The 1986 carburetor is the "feedback" version, whereas the 1981 model is not. The stock 1986 model carburetor was controlled by the EEC-IV computer, while the 1981 is a conventional, stand-alone version. The two are NOT interchangeable!
When the 1981 motor was brought in for a replacement, what else from the 1986 motor was retained besides the carburetor?
Originally Posted by broncoman72
if i rember right the motor is out of a 81 ford f150 and he is running the 86 carb
When the 1981 motor was brought in for a replacement, what else from the 1986 motor was retained besides the carburetor?
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Freshman User
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Sorry about the punctuation. Ill try to do better but info is more important than puctuation and run on sentences. I do appreciate any ideas and thank you again. Not a real good speller neither and not really computer savy either.
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Joined: Jun 2017
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Without proper punctuation and separating your sentences, it is very difficult to read your post, broncoman72. Try proof reading what you write before you submit your questions in the future. You will probably get more responses.
Therein probably lies your problem. The 1986 carburetor is the "feedback" version, whereas the 1981 model is not. The stock 1986 model carburetor was controlled by the EEC-IV computer, while the 1981 is a conventional, stand-alone version. The two are NOT interchangeable!
When the 1981 motor was brought in for a replacement, what else from the 1986 motor was retained besides the carburetor?
Therein probably lies your problem. The 1986 carburetor is the "feedback" version, whereas the 1981 model is not. The stock 1986 model carburetor was controlled by the EEC-IV computer, while the 1981 is a conventional, stand-alone version. The two are NOT interchangeable!
When the 1981 motor was brought in for a replacement, what else from the 1986 motor was retained besides the carburetor?
FTE Legend
Joined: Nov 2015
Posts: 30,863
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From: Angier, NC
Big if the carb has wires I am pretty sure it is a computer controlled carb and may not work like it should.
What was wrong with the 81 carb or that was not part of the motor deal?
What other things were changed from when you heard it run?
You may want to put the motor & carb year in your other post as I thought you took that running motor you bought and dropped it in your truck and now it is not running smooth and has a knock.
Dave ----
What was wrong with the 81 carb or that was not part of the motor deal?
What other things were changed from when you heard it run?
You may want to put the motor & carb year in your other post as I thought you took that running motor you bought and dropped it in your truck and now it is not running smooth and has a knock.
Dave ----
New User
Joined: Jun 2017
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Big if the carb has wires I am pretty sure it is a computer controlled carb and may not work like it should.
What was wrong with the 81 carb or that was not part of the motor deal?
What other things were changed from when you heard it run?
You may want to put the motor & carb year in your other post as I thought you took that running motor you bought and dropped it in your truck and now it is not running smooth and has a knock.
Dave ----
What was wrong with the 81 carb or that was not part of the motor deal?
What other things were changed from when you heard it run?
You may want to put the motor & carb year in your other post as I thought you took that running motor you bought and dropped it in your truck and now it is not running smooth and has a knock.
Dave ----
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
The 1984 F150 came with computer controlled carburetor and distributor. If the original distributor and carburetor are being used, all electrical and vacuum connections must be in place and functioning or the computer will lock the static timing and adjust the carburetor to run rich.
FTE Legend
Joined: Nov 2015
Posts: 30,863
Likes: 4,108
From: Angier, NC
The 1984 F150 came with computer controlled carburetor and distributor. If the original distributor and carburetor are being used, all electrical and vacuum connections must be in place and functioning or the computer will lock the static timing and adjust the carburetor to run rich.
I say if you have the dist that came with that motor put that back in and see how it runs and if still bad get a non-computer controlled carb then you only need 2 or 3 vacuum lines for the motor to run good.
Dave ----
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