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Yamaha YZ125CC Shifter Engines for 2002.

Yamaha introduced a new 125CC Shifter Kart Engine for 2002. Yamaha provide us a set of specifications and details concerning the 2002 engine which we reviewed with an engine builder from New Hanpshire who is highly skilled with YZ125's. We were interested to learn how the Yamaha factory was providing upgrades and improvements in response to input from Karting teams who have been fielding their engines for the past several years. We began using the YZ 125 in competition in1999 and we have been racing YZ125's built by Bill Price Racing for the past three years.

For 2002 Yamaha has provided assistance to the race teams in four major areas:

1. New cylinder design: added a third scavenging port and to alter the exhaust port shape.
2. Intake port design: Intake port has been bridged to improve reliability
3. New piston design: reposition the dent pin and widened the piston ring to 2.35mm width.
4. New carburetor: Cylinder side bore is increased to 40mm, needle and needle jet are redesigned.
5. New 8 bit micro ignition box: New size and new shape for the ignition box
6. Transmission changes: The YZ125 kart engine insides a six speed transmission.

The basic expectations for the 2002 offering are improved performance and reliability. This comes from new cylinder design and new piston design. The intake port has been bridged and the boost port enlarged to increase performance and to provide added reliability.

The carburetor improvements are opening the cylinder side bore diameter by 2mm. This should provide more consistent power across a broader RPM range. In some of the earlier versions there were some areas where there was a lack of crisp throttle response.

Acknowledging that there is a need to run well with a stock ignition box as well as with a re-programable box, Yamaha has redesigned the shape and size of the ignition box. The ignition curve that is delivered within the box has also been improved for the 2002 model. The 2002 box has an 8 bit micro computer within the ignition box

The 2002 YZ125 motorcycle is being delivered with a five speed transmission, the karting version of the 2002 YZ125 will continue to be delivered with a six speed transmission. This gives the karter the advantage of having more gear selections so that the driver can always maintain the optimum gear selection.

Another announcement that should please the racers is that Yamaha has indicated that they intend to maintain their pricing for the 2002 season. This is great news to race teams as the 2002 Yamaha is definitely a contender.

We have not yet had one of the 2002 YZ125's on the dyno at Bill Price Racing and as such we cannot give you the analysis concerning pipes. We also can not yet tell you what to expect with a re-programmable ignition. We learned that for the 1999, 2000 and 2001 Yamaha YZ125's that the hot pipe and silencers came from from RCE. The hot re-programmable ignition curves cane from Bill Price Racing and hot re-programmable ignition boxes came from Vortex.

As soon as we get a 2002 on the dyno we'll give a report and we'll then read the ignition box and tell you about the new ignition timing curve from Yamaha.

Bob Chiras
Crew Chief
All Kart International