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43 FUEL SYSTEM & EXHAUST
throat when the throttle is opened. The discharge
is prolonged by the pressure of the pump and the
restriction of the pump jet. This discharge allows
time for the high speed circuit to furnish neces-
sary fuel.
FIGURE 3
METERING RODS
The amount of fuel admitted to the carburetor
throat through the high speed circuit is controlled
by a stepped and tapered metering rod. Figure 2.
Opening the throttle raises the metering rod al-
lowing more fuel to pass through the jet.
At top speed the smallest section of the metering
rod is in the jet.
Under heavy load at part throttle and for acceler-
ation at part throttle, a richer than normal air fuel
ratio is required. To provide this richer mixture,
regardless of throttle position, the metering rod is
connected to a vacuum piston. Under normal
operating conditions the vacuum piston holds the
metering rod down against the throttle link. When
the engine vacuum drops, a spring under the
vacuum piston raises the piston and metering rod,
allowing more fuel to flow through the jet. As
soon as the engine vacuum rises, the need for rich
mixture passes and the vacuum piston returns the me-
tering rod to normal position for mechanical operation
through the throttle linkage.
CARBURETOR ADJUSTMENT
PUMP TRAVEL
1. Remove the carburetor dust cover and back out
throttle adjusting screw to seat throttle valve.
2. Pump connector link should be in the lower
hole (short stroke), Figure 3.
3. Pump travel should be 16/64". Use Carter
Universal Pump Stroke Gauge T-109-117-S if
available. Adjust pump travel by bending
throttle connecting link at lower angle. Figure
3.
FIGURE 4
METERING ROD SETTING
1. Remove air cleaner and carburetor dust cover.
2. Remove hairpin clip and disconnect spring from
metering rod and remove metering rod and disk.
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