How to Tune a Yamaha PW50by William Machin
The Yamaha PW50 has a two-stroke engine and automatic transmission. Fuel induction is provided by a Mikuni VM carburetor that operates with a linkage-cable system. Sensors provide data to a capacitor discharge ignition box that interprets the inputs and provides optimum fuel and spark to the cylinder. The motorcycle has a generator unit that takes the place of typical ignition timing, limiting a tuneup to carburetor settings and sensor maintenance. Tune your Yamaha PW50 for peak performance and head for the track or the trail.
Spark Plug and Sensors
Park the motorcycle on its center stand. Remove the spark plug-wire cap from the plug by hand. Loosen and remove the spark plug from the cylinder head with a spark plug wrench.
Gap the spark plug to 0.026 inches with a spark plug gap gauge. Reinstall the plug tightly in the cylinder head with the plug wrench. Reattach the plug-wire cap by hand.
Detach the wire lead at the fuel sensor on the right side of the cylinder head by hand. Loosen and remove the sensor with a metric wrench. Clean the inner end of the sensor with spray cleaner. Reinstall the sensor securely with the wrench. Reattach the wire lead.
Detach the wire lead at the exhaust sensor at the underside of the muffler by hand. Loosen and remove the sensor with the metric wrench. Clean the inner end of the sensor with spray cleaner and reinstall the sensor securely. Reattach the wire lead.
Throttle and Carburetor
Take a position where you can observe the throttle linkage at the left side of the carburetor. Twist the throttle grip at the handlebars slowly as you observe the action of the linkage.
Tighten the cable adjuster at the top of the carburetor with a metric wrench in small increments so the linkage responds immediately as you open the throttle.
Start the engine and allow it to warm up for three minutes. Locate the smaller idle-adjustment screw and the larger fuel-air adjustment screw at the right side of the carburetor. Turn the idle-adjustment screw to the right one full turn with a screwdriver.
Turn the fuel-air adjustment screw to the right or left with a screwdriver as you listen to the engine's speed. Turning it too far either way slows the engine's speed. Find the point where the engine idles at the fastest speed.
Allow the engine to idle. Turn the idle-adjustment screw to the left one full turn.
- Always adjust the throttle linkage before tuning the carburetor.
- Replace the spark plug every 50 hours to ensure the best performance.
- Remove and clean the carburetor every 200 hours for maximum fuel efficiency.
Things You'll Need
- Spark plug wrench
- Spark plug gap gauge
- Metric wrench
- Spray cleaner
William Machin began work in construction at the age of 15, while still in high school. In 35 years, he's gained expertise in all phases of residential construction, retrofit and remodeling. His hobbies include horses, motorcycles, road racing and sport fishing. He studied architecture at Taft Junior College.