Figure 12-12. Step-Up Piston.
(4) Press the step-up piston all the way down and push
moderately on the rod lifter tab so that you can tighten the
Figure 12-14. Measuring the Accelerator Pump Stroke.
(3) To adjust pump travel, loosen the pump arm
adjusting lock screw and rotate the sleeve until the proper
measurement is obtained; then tighten the lock screw.
12-5. Choke Vacuum Kick Adjustment.
The choke diaphragm positions the choke valve within
the air horn. Energize the diaphragm to measure the
vacuum kick adjustment.
a. Open the throttle valves and close the choke.
Release the throttle first, then release the choke.
b. Disconnect the vacuum hose from the carburetor
and connect it to the hose from the vacuum supply
(tool C-4207-A) with a small length of tube acting as a
fitting. Apply 15 inches of vacuum.
c. Insert a 0.110-inch feeler gage between the choke
Apply sufficient closing pressure on the lever to which
Figure 12-13. Adjusting the Step-Up Piston.
the choke rod attaches to provide a minimum choke
b. Adjusting the Accelerator Pump Stroke. Determine
valve opening without distorting the diaphragm link.
the accelerator pump stroke by measuring the distance from
The cylindrical stem of the diaphragm link will extend
the air horn surface down to the top of the accelerator pump
as the internal spring is compressed. This spring must be
shaft at the idle screw. To establish an approximate idle on
fully compressed to measure the vacuum kick adjustment.
newly assembled carburetors, do the following:
(1) Back off the idle speed adjusting screw to
completely close the throttle valve. The fast idle cam must
be in the open choke position.
(2) Turn the idle screw clockwise until it just
contacts the stop.
(3) Continue to turn two complete turns.
c. Adjusting the Accelerator Pump.
(1) Be sure the accelerator pump "S' link is in the
outer hole of the pump arm.
(2) Measure the distance between the surface of the
air horn and the top of the accelerator pump shaft (figure
12-14). The accelerator pump
setting at idle should