*New* Yamaha YZ125 2005-2018 V-Force 4 Reed Valve V4R04, Reed Valve, V-Force  - Langston Motorsports

*New* Yamaha YZ125 2005-2022 V-Force 4 Reed Valve V4R04

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New and Improved Yamaha YZ125 V-Force 4R Reed Valve System

The Yamaha YZ125 since it's re-birth in 2005 has been the go to Motorcycle for serious racers.  With a solid stock racing motor, the stock reed valve lacks that proper control of it's fuel-air mixture to the cylinder.  This is where V-Force Reed Valve System compensates for that.  With it's patented Reed Valve technology, it promotes significant increase in performance from bottom end to top end.  

Applications: Yamaha YZ125
Model Years: 2005-2018

The all-new VForce4R for the Yamaha YZ125 offers enhanced reed petal life as well as all the added benefits of the unique VForce reed valve design.

The unique design of the VForce reed valve system features double the reed tip surface over a conventional reed valve design. This has two major benefits: 1) The reed petals only travel half the distance as a conventional reed valve design to get the same airflow. 2) Because the reed petals only need to travel half the distance of that on a conventional reed valve design, there is a greater chance of them being fully opened as well as a better chance of sealing when they are "closed". A reed petal never truly "closes" in a classic sense, as it is always in movement. Consider this, an engine operating at 8,000 RPM results in a reed petal opening and closing 133 times in one second. This fact, sheds light on another VForce advantage. Since the petals are only traveling half the distance, they generally last longer are they receive less wear than the reed petals on a conventional reed valve design.



  • Double the reed tip surface over a conventional reed valve design
  • Increased bottom end, stronger mid-range and longer top-end
  • Greater efficiency due to reduced reed petal travel
  • More airflow means more horsepower
  • Reduced reed petal wear
  • Screw free design eliminates risk of screws going through motor
  • Screw free design enables rapid reed petal changes



  • All-new reed petal resin system, carbon fiber and lay-up
  • Pre-curved reed petal ensures better seal at tip
  • Wider reed cage for maximum airflow
  • Combined reed tip area increased by 10.5% resulting in increased total air flow
  • Airfoil shape added to cage tip to increase air velocity from outer ports
  • Long reed stops added to progressively slow petal tip velocity, for increased petal durability
  • Reduced frontal area of central wing by 15.6% combined with a more aerodynamic shape



  • Rubber overmodling on reed tip surface of cage to further enhance petal life
  • Pre-curved reed petal ensures better seal at tip



Moto Tassinari and VForce4R decals, detailed installation instructions, complete VForce4R reed valve system (including reed petals) and gaskets.