One of the most common problems on almost any carburetor is when the accelerator pump circuit fails to deliver the correct amount of fuel. The accelerator circuit works, you guessed it, when accelerating. Throttling up requires an extra shot of fuel and the accelerator pump forces that extra fuel up through the main discharge and out the venturi, mixing with the fuel already being delivered to the engine.
(a) illustrates the main discharge hole. This hole will either have a ball and weight, or a ball and spring. Replace with the same combination. Check ball 1st, then either the spring, or the weight.
There are several things to think about when rebuilding your carburetor, especially around the accelerator pump circuit. Make sure the pump well is polished so that the pump cup glides smoothly and clean out all of the small passages in the venturi. Using thin wire is about the only way, since cleaners and compressed air are not going to remove all of the ethanol deposits left behind.
With everything clean and you are ready to assemble the carburetor, it is a good idea to test the accelerator pump circuit before closing up the carburetor.
Test your accelerator pump circuit as follows:
- Fill the float bowl with liquid. We use mineral spirits.
- The accelerator pump well should fill up with liquid.
- Insert the pump and press down. Liquid should come out of the main discharge.
- Replace the check ball.
- Hold the check ball down with a brass drift punch (gently).
- Again, press down on the pump. You should feel a slight resistance since the check ball is not allowing liquid up through the discharge hole. If no resistance, then gently tap the check ball and the drift punch in order to seat the check ball.
- Install the venturi cluster and gasket.
- Press down on the pump again. You should get a good squirt out of the venturi. If not, then the passages are plugged. Use thin wire to clean out the passages.
With the test above completed you can feel confident that the accelerator pump circuit is going to perform as it should.