While uncommon, some items may ship from a separate warehouse

Transform your 1998-2004 Yamaha YZ125 with this Black Cover Upgrade Kit, combining Boyesen’s Factory Clutch Cover (CC-31B), Factory Ignition Cover (SC33B), and the Supercooler Water Pump Cover & Impeller Kit (WPK-31B).

Each cover is crafted from high-grade aluminum to guard your engine’s internals against dirt and water, ensuring a perfect leak-free seal.

Meanwhile, the water pump’s patented nautilus-style impeller delivers more consistent cooling by increasing coolant flow at all RPM ranges.

Each part features a tough black powder-coated finish for durability and a professional race-inspired look.

Item Specifics:

1. SC33B Factory Ignition Cover

   • Brand: Boyesen
   • Color/Finish: Black / Powder-Coated
   • Features:
     • Seals properly to protect engine internals
     • Strong, lightweight aluminum construction
     • Resists weathering, wear, and tear

2. CC-31B Factory Clutch Cover (0940-0392)

   • Brand: Boyesen
   • Color/Finish: Black / Powder-Coated
   • Features:
     • Guaranteed not to warp over time
     • Individually surfaced for a leak-free fit
     • Durable finish resists weathering

3. WPK-31B Supercooler Water Pump Cover & Impeller Kit (0940-0399)

   • Brand: Boyesen
   • Color/Finish: Black / Powder-Coated
   • Features:
     • Aluminum investment-cast cover and impeller combo
     • High-flow design tested to increase coolant flow
     • Patented nautilus-style impeller for better temperature control
     • Improves overall engine life

Fitment Table:

(Ensure your specific year and model match for proper compatibility.)

Note:

• Each cover is sold as part of this combined kit to deliver a complete blacked-out engine upgrade.
• If you have questions regarding installation or fitment, consult your service manual or contact a professional.

Upgrade your Yamaha YZ125 with this premium black cover kit—boost performance, protection, and style!

About the 1998-2004 Yamaha YZ125

The 1998–2004 Yamaha YZ125 is one of Yamaha’s most respected and beloved two-stroke motocross bikes, renowned for its light weight, sharp handling, user-friendly engine performance, and exceptional reliability. During this period, Yamaha significantly improved the YZ125, making it one of the most competitive 125cc two-strokes available, appreciated by both amateur and professional racers.

Here's a detailed overview of the 1998–2004 Yamaha YZ125:

Overview and Historical Context:

Between 1998 and 2004, the Yamaha YZ125 evolved from a capable but somewhat dated motocross bike into arguably the top 125cc two-stroke in its class. Yamaha placed great emphasis on refining engine performance, chassis handling, and suspension technology, particularly following the introduction of four-stroke competition in the early 2000s.

The YZ125 quickly gained a reputation for being an easy-to-ride, durable, and powerful small-bore motocrosser. Its competitive versatility made it highly attractive to both young racers stepping up from smaller bikes and veteran riders seeking a fun, lightweight option.

Engine and Performance:

• Engine Specifications:

  • 124cc single-cylinder, liquid-cooled two-stroke
  • Yamaha Power Valve System (YPVS) for broad, usable powerband
  • Reed-valve intake, typically Mikuni TMX carburetor
  • 6-speed close-ratio transmission

• Performance Traits:

  • Excellent mid-range to top-end power, smooth and progressive delivery
  • Noted for responsive throttle action and manageable power, suitable for riders of varying skill levels
  • Considered among the easiest to ride competitively, thanks to its predictable, linear powerband and reliability

Chassis, Suspension, and Handling:

• Frame and Chassis:

  • Lightweight steel frame with progressive refinements in rigidity, geometry, and weight savings
  • Excellent cornering agility, stability at high speeds, and confidence-inspiring ergonomics

• Suspension Components:

  • Front: Fully adjustable KYB inverted cartridge forks, praised for plush initial travel and progressive damping
  • Rear: KYB shock with linkage-type rear suspension, fully adjustable (compression, rebound damping, spring preload)
  • Consistently regarded as class-leading suspension performance throughout this era, especially from 2001 onward

• Braking System:

  • Nissin hydraulic disc brakes front and rear, offering excellent braking power and modulation

Evolution by Year (1998–2004):

1998–1999:

• Redesigned chassis for improved handling and stability
• Engine refinements to improve midrange and top-end performance
• Updated suspension settings for enhanced comfort and track feel

2000–2001:

• Introduction of significant engine updates: improved cylinder porting and power valve adjustments for increased power throughout the RPM range
• Major suspension and chassis refinements enhanced ride comfort, control, and maneuverability
• 2001 model is notably desirable due to refined power delivery and handling improvements

2002–2004:

• Continued refinements in chassis geometry and ergonomics for greater rider comfort and easier handling
• Engine further improved with revised cylinder port timing and better carburetor tuning for stronger mid-to-top-end pull
• Final steel-frame YZ125 generation before Yamaha’s major aluminum-frame redesign (introduced in 2005)

Racing Heritage and Legacy:

During this period, the YZ125 became a top choice for amateur racers due to its combination of excellent performance, rider-friendly nature, and reliability. Yamaha secured numerous amateur national championships in the U.S., particularly at Loretta Lynn’s AMA Amateur Nationals, reinforcing the bike’s reputation.

The YZ125’s competitive edge and reliability made it a popular choice for privateer racers in professional racing circuits, even as four-strokes began dominating factory-level competition.

Collectibility and Market Popularity:

The 1998–2004 YZ125 continues to enjoy strong popularity among amateur racers, vintage motocross riders, and collectors.

• Most Collectible and Desirable Models:

  • 2001–2004: Particularly noted for advanced suspension, refined chassis handling, and improved engine performance.
  • 2004 Model: Last steel-frame year, making it a notable collector’s item before Yamaha transitioned to aluminum frames in 2005.

• Aftermarket and Parts Availability:
  Excellent aftermarket support, readily available OEM and aftermarket parts, facilitating easy restorations and continued racing.

Common Maintenance and Issues:

• YPVS Power Valve Maintenance:
  Regular cleaning and service (every 20–30 riding hours) essential to ensure optimal performance.

• Top-End Rebuild:
  Recommended every 40–60 hours of riding, depending on use.

• Suspension and Bearings:
  Frequent fork seal and rear linkage maintenance required for continued smooth handling.

• Carburetor Jetting:
  Careful tuning ensures optimal performance, particularly with weather and elevation changes.

Conclusion:

The 1998–2004 Yamaha YZ125 remains one of Yamaha’s most celebrated motocross bikes, remembered fondly for its easy rideability, robust reliability, sharp handling, and exceptional performance in the competitive 125cc class. Its legacy continues today, cherished by enthusiasts for vintage racing, competitive amateur motocross, and sheer two-stroke fun.

Let me know if you’d like to dive deeper into a specific model year or particular detail!