4100 Accelerator Pump Circuit

This video illustrates how the accelerator pump circuit works on 1964 and later 4100 carburetors.

1964 & later

How the accelerator pump circuit works:

When you let up on the throttle the check valve opens and fluid fills the pump chamber.
Pressing on the accelerator puts pressure on the check valve to close it and forces fuel through the bottom hole into the main discharge passage and out the main discharge.



The new check valve has a long stem which you insert into the hole, then pull it through until the umbrella is all the way seated. Trim the stem off so that it doesn't intrude on the float.

4100 Check Weight measurements. Length is important because it needs room to move up when the check ball moves up to let fuel in.
You can buy a new weight here.

This means the diaphragm cover is warped. Remove the cover and run a flat file over the side that goes against the carburetor. You will find the high spots are at the screw holes. Don't take anymore material than you have to. You can also sandwich the cover between flat stock, put in a vise and heat up. Tighten the vise a bit and let is cool.