Owners manual

10
3. To adjust, shut down the engine.
4. Loosen the lock screw on top of the fuel bowl just enough to allow you to turn the adjusting nut. Hold the screw in position
with the screwdriver.
5. Using a 5/8” wrench, turn the adjusting nut in the appropriate direction: Clockwise to lower fuel level and counterclockwise
to raise the fuel level.
NOTE: Many customers attempt to adjust the float level down by turning the adjusting nut clockwise, only to see the fuel level
rise through the sight glass. This is due to the float being pushed down into the fuel, therefore displacing the fuel to a
higher level. You will find it easier to adjust the float levels, if you rev the engine slightly between adjustments to
evacuate the fuel.
6. Turn the adjusting nut in increments of 1/4 of a rotation.
7. Retighten the lock screw.
8. Restart the vehicle and observe the sight window.
9. Repeat steps 1 through 8 as necessary.
SECONDARY FLOAT LEVELS:
Very little fuel is drawn out of the secondary fuel bowls during idle operation. This makes it a little tricky to set the proper float
level with the sight glasses. Many customers attempt to adjust the rear float level down by turning the adjusting nut clockwise,
only to see the fuel level rise through the sight glass. This is due to the float being pushed down into the fuel, therefore
displacing the fuel to a higher level. You will find it easier to adjust the float levels, if you rev the engine slightly by opening the
secondaries between adjustments. This can be easily done by rolling the secondary throttle shaft linkage forward on the driver’s
side of the vehicle. This will use fuel from the secondary bowl at a much faster rate, allowing the float level to seek the
adjustment point that you have set. Once the floats have been set with this procedure, drive the vehicle, and recheck the float
level.
ACCELERATOR PUMP TUNING:
The accelerator pump’s purpose is to make up for the lag in fuel delivery to enable the engine speed to increase in response to
throttle opening. Differences in vehicle weight, transmissions, and rear axle ratios affect the amount of fuel and the delivery rate
that should be provided by the accelerator pump. This may necessitate the customizing of your accelerator pump to your
vehicle and its use.
NOTE: The old saying, “if a little is good, a lot is better”, does not apply to the proper tuning of the accelerator pump.
Your car’s performance can be just as bad if it receives “too much fuel too soon” as if it receives “too little fuel
too late.”
Two factors that affect the accelerator pump’s delivery are the pump cam and the pump shooter (discharge nozzle). The pump
cam determines the total volume of fuel and affects delivery rate; the pump shooter affects delivery rate and helps determine the
duration of the shot.
In general, the #1 location on the pump cams provides a moderate initial delivery and has a greater final delivered volume. The
#2 locations on the pump cams provide a greater initial delivery and have a lesser total delivered volume. The pump shooters
have a number stamped on their casting, which designates the shooter size in thousandths of an inch, i.e., a #25 shooter has a
.025” discharge orifice. The smaller diameter nozzles lengthen the pump shot duration and are used with heavier vehicles or
with vehicles equipped with lower numerical rear axle ratios. Larger diameter nozzles (.035 - .037) shorten the pump shot
duration, but deliver a greater initial volume of fuel. These sizes should be used on applications where engine speed will
increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the accelerator pump delivers
the lean, best-power, air/fuel ratio to the engine; not when the maximum volume of fuel is supplied.
An important point should be kept in mind when tuning a Double Pumper™; the secondary accelerator pump must supply fuel
for a sufficient time so that the secondary main nozzles can “start up” and deliver fuel to the engine after the secondary throttle
plates are opened. If the nozzles do not start by the time the pump shot expires, bogging will result. To apply the information
above, follow these steps for tuning the accelerator pump.