CARBURETOR 71

 
6. The needles are fastened in the slide with a clip in one of three groves.  Changing the clip to a lower groove raises the needle and enriches the mixture.  Lowering the needle leans it.  Remember, raise to richen and lower to lean.

Slide and Mid-Range Metering System

1. This system operates from 1/4 to 1/2 throttle opening.  The air flow is controlled by the slide, with little effect from the cutaway (see Figure 3, page 72).  Fuel is withdrawn from the mid-range needle jet by the vacuum.

2. The needle is withdrawn halfway from the jet and it becomes the primary fuel metering device at this throttle opening.

3. A booster system is provided to help the mid range jet at 1/2 opening.

4. Air enters the booster hole and enters the midrange jet through small holes drilled half way up it. This boosts the fuel flow into the engine.

5. The  booster is adjustable on the 1971 250 Pioneer.  Air enters the booster hole (see Figure 4) and flows past a metering screw to the jet.  Turn screw clockwise to lean the mixture and counterclockwise to enrich it (Figure 5, page 73).

6. The mixture can be controlled by changing the mid-range needle jet or the mid-range main jet to a larger or smaller size. 

7. The 1972 Pioneer and Stiletto 175 and 250 models do not have a booster system (see Figures 6 and 7).

8. The mixture control at 1/2 throttle affects the mixture at wider settings.

 

Slide Cutaway and High Speed Needle

1. This system operates at 1/2 to 3/4 throttle opening.  The cutaway directs air down on the high speed needle jet, reducing the vacuum and fuel flow (see Figure 8, page 74).  As the slide is raised, the air flow is horizontal across the jet, increasing the fuel flow.

2. The fuel flow is now regulated by the high­speed needle and jet.

3. The mixture can be controlled by changing the cutaway, but this affects the lower speed mixture also.

4. The mixture can be controlled by changing the high speed needle and jet. 5. The best method of control is to raise or lower the high speed needle, for richer or leaner mixture.

Slide and High Speed Main Jet

.1. This system operates from 3/4 to full throttle opening (see Figure 9, page 75).  As the slide is raised, the cutaway has less effect on the air flow.

2. The needle is raised until it has less effect in controlling fuel flow.

3. The high-speed main jet now controls the fuel flow.

4. To control the mixture, change the high speed main jet to a larger or smaller size to enrich or lean the mixture.

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