Carter YF & YFA Check Ball & Check Weight

Carter YF & YFA Check Ball & Check Weight Placement

1st of all we should know what the check ball & check weight is for. When you press on the gas to accelerate, the engine needs an extra spurt of gas to get you accelerated until the cruise circuit can catch up. This is where the accelerator pump circuit comes in play. Pressing the accelerator causes the accelerator pump diaphragm to move up forcing a small amount of fuel out through the main discharge. The force of this fuel forces the check ball and check weight, or in some cases just the check weight up, allowing fuel to flow through the main discharge. When gas isn’t being pushed out the discharge, the check ball closes off the fuel so that vacuum from the intake doesn’t siphon fuel through the main discharge.

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 Ball

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.

Carter YF Check Weight

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

YF Main Discharge

Carter YF Discharge

Updated on 04/13/2022

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