Testing the accelerator pump circuit on a Rochester 2 Jet carburetor.

This article only refers to the type of 2 jet that uses a check ball in the bottom of the pump well. Not all carburetors do.

When rebuilding your 2 jet you may want to test the accelerator pump circuit before closing up the carburetor. Here are the steps you need to take.

Place the smaller and aluminum (when provided), check ball into the bottom of the accelerator pump well.

Fill the float bowl and the pump well with mineral spirits.

Put the pump in the well and push it down toward the bottom of the well. The check ball will seal the hole, keeping the fluid from going back into the float bowl and the fluid will be forced through the 2nd hole through the main discharge. You should see fluid come out of the main discharge.

Now test to see if the check ball seals by holding your finger over the main discharge hole and pressing down on the pump again. You should feel a slight pressure on the accelerator pump and there should not be any bubbles or some other sign that would indicate the check ball is leaking and fluid is being forced backwards.

The larger check ball in the main discharge tube must also be tested. Hold the check ball down with a brass drift punch and push the accelerator pump down. You shouldn’t get but a slight amount of fluid past the check ball.

To re seat a check ball, using a brass drift punch, hold the check ball down into the hole with the drift punch and tap a few times with a hammer. Don’t get carried away, or you will get the check ball stuck. The hole in the carburetor you are trying to form is soft metal and doesn’t take much to change.

Now you can be confident your accelerator pump circuit is doing what it should.