1. This system operates from 3/4 to full throttle (see Figure 15).

2. As the needle is withdrawn from the needle jet, the main jet controls the fuel flow. 3. To adjust the mixture, change the main jet to a larger or smaller size for richer or leaner mixture.

Float Metering Device

1. As the fuel flows into the float bowl (see Figure 16), the float is raised.

2. This closes the float needle in the metering jet, stopping the flow.

3. The constant level and constant pressure provides even fuel flow through the carburetor.  Adjustment is detailed below.

Carburetor Adjustment and Tuning

1. Be sure all other engine tune-up procedures are completed first.  Tune the carburetor last.

2. Be sure the air cleaner is clean and the filter screens on the petcocks and carburetor banjo are not clogged.

3. Check the breather tube on the fuel tank for clogging.

4. Check the spark plug for type and heat range.

5. Check the ignition components and timing.

6. Check all gaskets and nuts for fit and tightness.

7. Check the piston, rings and cylinder clearance for wear or damage.

8. Check the carburetor for cleanliness and fuel or air leaks.

9. Check the exhaust system for proper type and freedom from restrictions.

Rough Tuning

1. Warm up the engine to operating temperature.  On a level or slightly uphill grade, run the engine up to peak rpm by opening the throttle slowly and smoothly.  Then close it slowly and smoothly while listening carefully.

2. If the engine pings or rattles, the mixture too lean.  If it dies or loses rpm while opening the throttle, it is very lean.  Note at what throttle opening these symptoms occur.

3. If the engine four strokes, firing every other revolution, or accelerates poorly, the mixture is too rich.  If the exhaust has excessive smoke when the fuel/oil/ratio is correct, the mixture is too rich.  Note at what throttle opening these symptoms occur.

4. Wrap white tape around the twist grip (see Figure 17) and divide it with marks designating throttle openings.  Mark the throttle housing seam as the reference point with an arrow.  By glancing at the throttle, you know what the throttle opening is where the symptoms occur.

5. For lean running at all throttle settings, re. move the float bowl and check the float for proper operation.  The float must pivot freely and the needle seat in the metering jet properly.

6. Hold the float bowl with the float toward you (see Figure 18).  Pass a 1/4" rod between the small rib of the float bowl at I o'clock and the float body.  With the float upside down, the rod should pass between the rib and the float without moving the float.