This is an example of a 4300 carburetor. It has an air valve spring (1), with an idle mixture screw (2) instead of a throttle cracking screw, and also has the hot idle compensator (3)

The idle-mixture screw limiter caps are plain to see on this late model 4300. Note the three hole positions for the fulcrum pin in the accelerator pump arm. The different positions give a longer or a shorter stroke.

Also visible in this image is the rectangular ID tag held down by one bowl screw. This tag contains the OE Ford ID number which is what we use to identify the carburetor parts.

Shown here is an early model 4300 without the limiter caps on the idle mixture screws.

When you see this large screw in the end of the carburetor, it means that the throttles close almost completely at curb idle. This screw is the air bypass that regulates the idle speed of the engine.

The power valve is easily removable if you have a socket that is deep enough to clear the stem.

Located in the bottom of the bowl are the two main jets with the power valve positioned between them.

The screw indicated by the arrow on the 4300 is for fast idle adjustment only.

Float level on the 4300 is set with the bowl cover inverted, and the float resting on the closed needle. Measure distance from the bowl cover surface to the top of the float.

The air horn of the 4300 is much more than a cover, and contains many components. This early model example uses the external air valve spring.

This little link on the 4300 connects to a piston in a well of fuel. Secondary air valve works against the piston, opens slowly to eliminate bog.

Changing the float level on a 4300 is pretty tricky. It will be a lot easier to do if you first make this little bending tool from a piece of still wire.

Most carbs only have a single-needle valve, but the 4300 has two. It requires an additional adjustment for the second valve. With the float gauge in place holding up the floats, the second valve should clear by a certain amount according to your carb’s specifications.

Early model carburetors used a spring on the other side of the carburetor to close the air valve. Late models have done away with that external spring and instead use a spring underneath the piston. If your 4300 does not have the external spring, if must have this one under the piston, or the valve will stay open all the time.

On the underside of this bowl cover we see the stem of the vacuum piston which operates the power valve.

On a sidenote, pay special attention to your float alignment. You can see it’s a very tight fit in the bowl and if it rubs against the side, you’ll end up with a “stuck” float condition.

All of the bowl cover screws in the 4300 are the same, except this one - and it must go in this specific location.