YF Check Weight

What Is a Check Weight in a Carter YF Carburetor?

The check weight is a small metal component that sits on top of the accelerator pump check ball. Its function is to apply downward pressure on the check ball, helping to seal the fuel passage during pump stroke and allowing the fuel to be directed properly through the main discharge.

Check ball in the main discharge: 5/32

Check ball in the intake: 1/8

Without the correct check weight in place, you may experience:

  • Poor accelerator pump function

  • Engine hesitation during throttle tip-in

  • Delayed or weak fuel discharge

  • Air or fuel blowback in the pump circuit

Watch a video about the YF check weight.

Some Carter YF carburetors have a check ball with a check weight on top of it. See # 24 & 25 in the illustration below. Notice that the check weight is rectangular shaped. This check weight is nothing more than a weight. It probably weighs less than 1 gram, but that's OK. Too heavy and the check ball would not lift off the hole.


Carter YF Carburetor Check BallCarter YF Check Weight
Other YF & YFA's might have just a check weight, but this check weight is tapered on the end and this taper acts the same as a check ball does. See #26 in the illustration.
Check weight w/o check ball. There are 3 different lengths depending on the carburetor. Most use this one captioned here. After placing in the main discharge you should have 1/16 - 1/8" free space for the check weight to lift off the seat. You can grind the check weight down to fit.
Carter YF check weight
Check weight w/check ball. Make sure you have about 1/16" - 1/8" of free space for the check ball to lift up. If you need more, simply grind down the check weight to fit.When rebuilding your carburetor, test the accelerator pump circuit before installing the carburetor on the engine.

Add liquid to the float bowl. Push the accelerator pump down, then pull up. Pulling the pump up will force fuel out of the main discharge. If you don't see fuel coming out then you have a plugged passage. Use thin wire to clean out the passage way.


Using a brass drift punch and holding the check ball, or weight down to plug the hole, pull up the diaphragm again. You should feel a little pressure. If you get very little pressure, or fuel is coming out around the check ball, then you need to seat the check ball. Do this by inserting a brass drift punch on top of the check ball and tapping it a few times. This will seat the check ball. Now I said tap, not bang on it. You don't want it to get stuck.

Carter YF & YFA Parts

The check weight in a Carter YF carburetor is essential for proper fuel pump circuit operation. Whether your model uses the traditional check ball and weight combo or the newer pointed one-piece design, always use the correct part to ensure optimal performance.

Need the right check weight for your YF? Browse our selection of ethanol-resistant Carter YF carburetor parts today.

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