Idle Adjustment Screw
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Senior User
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Idle Adjustment Screw
I have a 2 barrel carb that doesnt seem to idle right, I cant seem to find any makers marks. There is a screw underneath the bowl, is this the idle adjustment screw ? if not where are they normally found on a 2 barrel carb ?
Lead Driver
Joined: Oct 1999
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From: Kalispell, MT
I'm not your best source of info, but since nobody else has jumped in here...........
A two barrel carb will have 2 idle adjustment screws - normally brass with a visible spring that provides tension to keep the adjustment where you set it. Usually are found in the carb base.
Not sure but I'd bet the screw on the bottom of the bowl is the mounting bolt?
A two barrel carb will have 2 idle adjustment screws - normally brass with a visible spring that provides tension to keep the adjustment where you set it. Usually are found in the carb base.
Not sure but I'd bet the screw on the bottom of the bowl is the mounting bolt?
Posting Guru
Joined: Jul 2001
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From: Southern New Hampshire
The 3 bolt carb used on Fords up thru 56-57 is adjusted from the rear but they are idle mixture adjustments, not idle speed. The idle speed screw is on the throttle shaft linkage and sets the correct point on a cam.
Those carbs usually have model ID on the bowl side, such as 8BA, EAB, ECG, 2100, etc. They are made by Holley and are part of the 94 family.
Those carbs usually have model ID on the bowl side, such as 8BA, EAB, ECG, 2100, etc. They are made by Holley and are part of the 94 family.
Lead Driver
Joined: Oct 1999
Posts: 6,782
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From: Kalispell, MT
Uh, I'm a little slow on the uptake - or maybe stuck in the 50's.....
Bet you're talking the 390 in your '60, huh?
Closest reference I have is a Haynes for 64-73 Mustangs. General info should still be good. Two bbl should have 2 idle mix adjustment screws - 1 for each bbl under the bowl
Sorry for the earlier confusion - must be time for my meds
Bet you're talking the 390 in your '60, huh?
Closest reference I have is a Haynes for 64-73 Mustangs. General info should still be good. Two bbl should have 2 idle mix adjustment screws - 1 for each bbl under the bowl
Sorry for the earlier confusion - must be time for my meds
Logistics Pro
Joined: Oct 2002
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From: Valley Center, CA
OK, what year engine? Make of Carb? If it's like my 2 barrel on my 272, then I adjust it with the engine running. I turn the screws in until the rpm starts to drop, then I back it out 1/2 turn. Then I adjust the second one. However, you also need to check that the choke is fully open, the air filter isn't plugged, and that you don't have a bad float. How long since this carb has been rebuilt? Do you have a good fuel filter? Good luck, John
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I'm a newbie concerning auto repair, so I'm learning as I go. It's for a 390, there are no maker's marks on the carb. I just replaced the filter and I have no idea when it was rebuilt. As for "basic details", this is as good as I can do .Thanks for the help.
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Logistics Pro
Joined: Oct 2002
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From: Valley Center, CA
Wow, talk about the blind leading the blind. Well, besides the prior info, all I can advise is to be incremental in your changes to the carb and to keep notes on what you change. That way if worse comes to worse, you can at least eset it back to where it was when you started. Good luck, John 
Posting Guru
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From: Southern New Hampshire
Well, 390 is a start and there should be some info either on the airhorn or the top of the bowl. ID codes would be something like "CODE 9510", "C4AF-B", and so on.
Odds are it is a Ford/Autolite which is a very easy carb to work on.
For starters the idle mixture screws will be in the 1 to 1 1/2 turns open range for proper adjustment. Turn both screws in until they stop (DO NOT force) and then back them both out 1 1/4 turns. Then you can turn a hair either way until you get the best idle. If the screw(s) have no or little effect then the carb needs a cleaning.
If you plan on getting your hands dirty then invest in either a shop manual for the year of the engine or at least a 60's Motors manual. If the carb is from the smog era, get rid of it and find an earlier one or an aftermarket replacement. The code will tell the year and application.
Odds are it is a Ford/Autolite which is a very easy carb to work on.
For starters the idle mixture screws will be in the 1 to 1 1/2 turns open range for proper adjustment. Turn both screws in until they stop (DO NOT force) and then back them both out 1 1/4 turns. Then you can turn a hair either way until you get the best idle. If the screw(s) have no or little effect then the carb needs a cleaning.
If you plan on getting your hands dirty then invest in either a shop manual for the year of the engine or at least a 60's Motors manual. If the carb is from the smog era, get rid of it and find an earlier one or an aftermarket replacement. The code will tell the year and application.
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