carburator setting

[mikes4692003]

can somebody tell me how to adjust the air and fuel screws on a 1969 383 with a 4 barrel carter carburator the numbers on it are f64734st?

[Musicman]

First off... I congratulate you already just for asking the question... Most folks do not realize how important it is to get the idle circuit of their carburetor set up correctly.

OK, here is the right way to do it... If you don't have a tach just listen to the engine and play it by ear, but a vacuum gage should be used.


To begin, make sure the engine is up to full operating temperature and the choke is completely off. A cold engine requires more fuel than a fully warmed engine even if the choke is off. Remove the air cleaner and connect the tach to the engine, and the vacuum gauge so it reads manifold vacuum.

Before you fire up the engine, slowly turn each idle-mixture screw in until it gently bottoms out and count the number of turns it takes. Do this for each idle-mixture screw and then return them to their original positions. If all the idle-mixture screws are not adjusted the same, do that now. Remember to always adjust both screws the same amount. This will help balance the idle mixture and allow the engine to run as smoothly as possible. If the carburetor is new to the engine, start at 1½-turns out (counterclockwise) from full in.

Now start the engine and set the idle speed to around 850 - 900 rpm's or so with the curb idle-speed screw. If your engine has a big cam and must idle at a higher speed, that's OK. Note the reading on the vacuum gauge. Next, very slowly turn one idle-mixture screw in ½-turn and note the change on the vacuum gauge. If the vacuum reading increases say, from 14 inches to 14-½ inches, move around to the other side of the carburetor and slowly turn that mixture screw in ½-turn as well. If the engine stumbles or the vacuum drops when initially turning the mixture screw in, turn both screws out about a ½-turn and evaluate the results. On most carburetors, turning the mixture screw in (clockwise) leans the mixture, while counterclockwise (out) enriches the mixture.

The goal of adjusting the idle-mixture screws is to achieve the highest possible idle vacuum at a set idle speed. If the idle speed increases after you adjust the idle-mixture screws (which is likely), be sure to adjust the curb idle speed screw back to the base speed again before moving forward. This is important because a higher idle speed will increase the vacuum reading. Maintaining a standard idle speed will make it easier to evaluate changes to the idle-mixture screws.

[GN]

Can this method be used on a 2brl carb too?

[Tilar]

Yup.