Yamaha YZ two-stroke flat on top: clean the YPVS power valve

Applies to: Yamaha YZ125, YZ250 and other two-strokes with power valves

Symptoms

  • Pulls fine low, goes flat on top
  • Sluggish response, wet exhaust
  • Hasn't had the power valve cleaned in a season

Why it happens

Carbon from two-stroke oil builds up on the power valve and its linkage until it sticks, so the exhaust port never opens fully.

How to fix it

  1. Remove the power valve cover and linkage per the manual.
  2. Pull the valves and clean off carbon.
  3. Check the linkage, springs and governor for wear and free movement.
  4. Reassemble and check timing marks and smooth travel.

Tools and parts

  • Carbon cleaner
  • Gaskets and O-rings

What the factory service manual covers

Engine: YPVS removal, inspection and assembly. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.

Get the factory service manual

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