The model 1940 carburetor is assembled of three
major sub-assemblies. These assemblies are the air horn or
bowl cover, carburetor body assembly and throttle body
assembly. Servicing of the carburetor can be simplified if
these sub-assemblies are disassembled and kept together in
their respective groups.
THE FOLLOWING PROCEDURES APPLY TO THE MODEL
Remove nut and lockwasher retaining the pump
rocker arm and pump link.
Remove the bowl cover screws.
The position of the link in the rocker
arm slots and the position of the throttle return spring or
the positive throttle return spring on some model
applications for proper reassembly (Figure 9).
FIG.8. Accelerator Pump System
Separate the bowl cover from the carburetor body.
Do not pry. Tap gently from side to side with a plastic
REPLACING IDLE MIXTURE SCREW
hammer or screwdriver handle.
Reinstall the idle mixture screw and turn screw lightly
Remove the accelerating pump operating rod retainer
against its seat with the fingers. Back off the exact number of
screw and retainer.
turns recorded during disassembly. With the idle speed
Rotate the pump operating rod and disconnect the
screw backed off and throttle plate completely closed, check
pump drive spring and accelerating pump assembly
the PUMP PISTON STROKE ADJUTMENT (distance from the
(Figure 10). Set the pump assembly aside. Do not
vacuum passage casting to the center of the hole in pump
immerse in cleaner. A new pump cup is in the kit.
Rotate the pump operating rod and remove the rod
IDLE SPEED ADJUSTMENT
and grommet from the bowl cover (Figure 11 ).
A stop screw controls the engine idle speed Run the
With a hearing scraper or a scraper ground from an
engine until normal operating temperature has been reached
old triangle file remove all the staking from the
Turn the idle stop screw "in" to increase the engine speed and
vacuum piston retainer (Figure 12).
"out" to decrease the engine speed.
With a suitable puller or long nosed pliers and
CARBURETOR IDLE MIXTURE ADJUSTMENT
support, remove the vacuum piston assembly (Figure
Idle speed and fuel mixture
Remove bowl vent valve from rod if so equipped. The
rod cannot be removed.
adjustments must he made with the ENGINE AT NORMAL
Remove hot idle compensator valve cover, valve and
OPERATING TEMPERATURE and engine air cleaner in
gasket from cover. if so equipped.
This normally completes disassembly of the bowl
cover. If the carburetor is equipped with a mechanical power
I%-2% accurate and have expanded scale of 1-1000
valve modulator rod It cannot be removed.
or 400-800 RPM.
Unless the choke valve is bent or
Be sure engine is thoroughly warmed up. Adjust "idle
damaged DO NOT REMOVE the choke salve screws, valve
speed" screw to specified RPM per idle speed
or shaft for normal service.
Turn the mixture adjusting needle in until the engine
begins to run rough from the lean mixture. Slowly turn the
needle out until the engine begins to "roll" from the rich
mixture. Then slowly turn the needle in until the engine runs
smoothly. Always favor a slightly rich mixture rather than a
It may be necessary to reset the idle speed stop
screw after the correct idle mixture is obtained.
FIG.9. Remove or Install Accelerator Pump Rocker Arm.