5. The object of the combined systems is to have them blend together as the throttle is opened, and they should be adjusted accordingly.

Float Metering Device

1. This system provides a constant fuel level and pressure in the carburetor (see Figure 110, page 76) for even flow through the systems.

2. As fuel flows into the float bowl, the float rises and pushes the float needle into the intake metering jet, closing it to more fuel flow.  This system is adjustable, as detailed below.

SINGLE NEEDLE MODELS

Pilot Metering System

1. This system operates from 0 to 1/8 throttl e opening (see Figure. 11, page 77).  The fuel is metered by the pilot fuel jet and the air by the low-speed air screw and the carburetor slide.

2. With the engine idling, the up stroke of the piston creates a vacuum in the intake port.  This causes air to flow into the pilot air jet to the low­speed air screw and the pilot fuel jet.