Carburetor adjustment for the 4 barrel/390

[novanutcase]

Can anyone tell me the basics to adjusting your 390/4 barrel motorcraft carburetor. The adjustments that I know of are Choke, Idle, Air screw. Where should the choke be set to ideally? Can the Idle be adjusted by ear or is there a guidline to go by? If I'm facing the engine, what does the air screw to my left do? When you screw it in is it giving more or less air? Same question but for the right?

[Harley Eaton]

The question returns: do you have a shop manual? The choke adjustment should be outlined there. Specs will say idle should be adjusted to a specific RPM. The two idle mixture screws in the base of the carburetor control the air to the idle mixture. Screwing them in will allow less air. Screwing them out will allow more air. Usual adjustment is to screw the adjustment screw in until you detect a drop in the idle speed, then turn the screw out half turn. Then do the other and go back and check the first one.

[novanutcase]

Thanks Harley! I was playing around with the idle yesterday but when I was adjusting it the car was at operating temperature. I adjusted the choke two clicks towards the lean side from the center adjustment and the car seemed to run fine. Should I adjust the choke when the car is cold? As far as the air screws I turned them in all the way(Gently so that the screw doesn't get scored!) and turned them out a turn and a half with the idle screw set very low. I then turned the idle screw up and opened the right side air screw until the idle started to go up. I did the same turns for the other side and the idle went up higher then backed them both off around a 1/4 turn and the idle went down. Was this the right way to do it? I don't have a shop manual.

[Harley Eaton]

With the engine at operating temperarure, the choke butterfly shoud be completely open. With a completely cold engine, the choke should be completely closed. Be sure your choke heat tube is not obstructed. The main thing is that the car should start good when cold and not be running rich due to choke when warmed up.
I've never adjusted the idle mixture as you did. I turn the screws in until the engine speed start to drop off, then open slightly. Don't understand why you would stop opening the screws when the idle speed started in increase.(?)

[novanutcase]

Originally Posted by novanutcase

Thanks Harley! I was playing around with the idle yesterday but when I was adjusting it the car was at operating temperature. I adjusted the choke two clicks towards the lean side from the center adjustment and the car seemed to run fine. Should I adjust the choke when the car is cold? As far as the air screws I turned them in all the way(Gently so that the screw doesn't get scored!) and turned them out a turn and a half with the idle screw set very low. I then turned the idle screw up and opened the right side air screw until the idle started to go up. I did the same turns for the other side and the idle went up higher then backed them both off around a 1/4 turn and the idle went down. Was this the right way to do it? I don't have a shop manual.

Sorry, I explained it wrong! I didn't turn the idle screw up after it was set very low. I turned the AIR screw until the idle went to the desired idle and did the same for the other side. I then turned them a 1/4 turn back as the idle was a bit high after turning the second screw and set it there. It now starts without me pumping the gas and idles perfectly cold then drops to a nice clean, even idle.