When pressing down on the gas pedal, the engine hesitates then begins to catch up.
This could be caused by the distributor, but we will only address the carburetor.
Hesitation is generally due to the accelerator pump circuit.
- The pump could be bad – replace it.
- With the engine off look down the carburetor and pump the gas. You should see 2 good squirts coming out of the main discharge. – Using thin wire clean out the 2 discharge nozzles on #36. Ethanol can leave residue cleaners will not get out.
- Remove the pump jet housing. With fluid in the pump well, press down on the accelerator pump. Fluid should rush out of the main discharge. If it does, then the passage way from the pump well to the main discharge is OK.
- The check ball in the main discharge may not be working or missing – There should be a check ball and a spring, or a check ball and a check weight, or a check weight with a pointed end. See # 37 in the illustration. Depends on which AFB you have.
- Maybe the check weight, or check ball isn’t sealing – Hold down the check ball or check weight with a brass drift punch and press down the accelerator pump with fluid in the carburetor. We use mineral spirits. You should feel some pressure which means the check ball is doing it’s job. – If you get a leak, tap on the check ball a few times with the brass punch. It doesn’t take much pressure to form a seat for the check ball.
- Make sure the gasket under the pump housing #36 fits flat. Sometimes a new gasket will need to be trimmed so that it lays down flat.
- There is an off idle circuit that is often missed. Look for a hole just above the idle mixture hole inside the bore. Blow air through the hole to see if air gets all the way through to the top of the carburetor. This is used when transferring from idle to the accelerator pump circuit and can cause some hesitation.