The accelerating pump, which is connected by the pump link to the throttle lever, is actuated by throttle movement. When the throttle is closed, the pump piston moves upward, drawing fuel from the float chamber through the pump inlet and into the pump well. The pump inlet check valve opens to permit fuel to enter the pump chamber, and closes to prevent a reverse flow of fuel when the pump is operated. The upper end of the pump operating rod fits within a vertical slot in the pump piston stem and moves independently of the pump piston upon acceleration. When the throttle is opened, the pump operating rod is pulled down, compressing the pump spring. The pressure of the spring moves the pump piston downward, forcing fuel through the accelerating pump system. The spring overriding feature provides a sufficiently long interval of discharge, regardless of how suddenly the throttle is opened.
How To Test the Accelerator Pump?
With the carburetor installed and the air cleaner off, pump the throttle once and see if gas is being squirted into the bore. If not then you have have a problem with the pump, or one of the passages.
With the carburetor on the bench, fill the float bowl with mineral spirits. With the pump all the way down, pull up on the 885 accelerator pump and watch if the float bowl partially fills. If not, then check that the pump inlet ball check valve is in place and not stuck.
Hold down the discharge check ball and push the pump down. You should feel some pressure and not see much (if any) fuel come out of the main discharge.
Pump the pump to see if gas is being sent through the pump discharge.
