Yamaha YZ125

 

Introduction


During the second half of the nineties the Yamaha YZ125 has established an enviable track record throughout the motocross scene, culminating in its World 125cc Championship win last season. Undoubtedly one of the quickest production machines in its class, the YZ125 is also regarded as being one of the best handling bikes in this super-competitive category. This successful formula looks set to continue into 1999 with the arrival of the latest generation YZ125 which benefits from a wide range of engine and chassis improvements designed to keep this winning machine at the top.


For the 1999 season the Yamaha YZ125 engine features a number of significant changes which are designed to significantly enhance overall power output.

Exhaust port height and width is increased, and scavenging port is also reshaped and enlarged. YPVS mechanism has also been modified to improve sealing between the valve holder and cylinder, and for more efficient operation the YPVS governor is fitted with redesigned components. Complementing these changes to the cylinder and YPVS is a new lightweight exhaust featuring a revised taper profile and 10% thinner steel, as well as a factory bike replica tail pipe featuring a resin tail cap.

Intake efficiency on this advanced crankcase induction engine is enhanced for '99 by the fitment of a new, more compact TMX36mm carburettor fitted with a new-shape throttle valve. Together with a wider 43.5mm diameter inlet manifold and resized air-cleaner joint this new system makes for stronger, more responsive low to mid range power.

Crankcase design is also improved for the new race season by the use of a reshaped intake tract and an enlarged scavenging path which makes for enhanced performance at all engine speeds.

YZ125 Engine

Technical Changes - Highlights

Intake and exhaust ports reshaped and enlarged

Yamaha YZ125

 

Chassis


As well as the large number of chassis improvements found on both the YZ250 and YZ125, the 125 also features a relocated right side footrest moved 5mm higher, as well as a modified left side seat pillar tube which is moved away from the carburettor to facilitate removal.


Technical Changes - Highlights

 

Chassis