Section 11:

3/4 to Full Throttle: Slide and Main Jet

(Fig. 138)

1 . From 3/4 to full throttle, the additional flow of air is regulated by the position of the slide. As the slide nears the- top of the bore, the cutaway has little or no effect. A higher vacuum is then created at the needle jet, drawing out an increasing amount of fuel.

2. As the needle is raised higher in the needle jet by the upward movement of the slide, it becomes less effective in metering the flow of fuel accurately. From 3/4 to full throttle, the main jet controls the flow of fuel.

3. To vary the mixture from 3/4 to full throttle, fit a main jet with a higher number to make it richer, or with a lower number to make it leaner.

4. NOTE: Each metering system blends gradually with the one preceding it and the one following it. The objective of regulating the carburetor is to arrive at a condition wherein there is a smooth transition from one metering system to the next and the proportion of fuel and air remains the same from closed throttle to full throttle.

Section 12:

The Float Metering Device (Fig. 139)

1. The float mechanism provides a constant level of fuel for the fuel metering system. This constant fuel pressure allows for an even rate of flow through the jets.

2. When the fuel flows through the float metering jet in the top of the float bowl, the
fuel level in the bowl rises. This causes the float to rise and push the float needle up into the float metering jet. When the fuel reaches a predetermined point, the float will have risen to a point that is sufficient to fully seat the float needle in the metering jet, stopping the flow of fuel. Chapter 2, Section 2, Paragraph 9 covers the adjustment and maintenance of the float mechanism.

FIG. 139

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