Yamaha YZ
2-Stroke Engine Packages
The definitive guide on how to make your YZ faster with factory-level porting, head mods, and YPVS tuning.
YZ Factory Engine Services
The YZ65 entered the market with a massive advantage: the mechanical Yamaha Power Valve System (YPVS). Unlike its competitors, the YZ65 uses a ball-ramp governor for consistent valve opening. However, the stock port timing is often conservative to ensure reliability. We blueprint the YPVS mechanism to match our aggressive cylinder porting, turning a solid mini bike into a platform that pulls longer and harder than anything in the class.
- YPVS Blueprinting: Timing the mechanical governor for instant snap.
- Crankcase Stuffing: Increasing primary compression for better throttle response.
- Carburetor Jetting: Correcting the stock 'rich-bog' hesitation.
For years, the YZ85 was a 'lightswitch'—all top end, no bottom. The 2019+ update brought a power valve, finally giving it torque. Our engine packages are split into two philosophies: For 2019+ models, we optimize the YPVS to carry that new bottom end further into the over-rev. For older non-PV models, we perform extensive cylinder base work and head re-profiling to artificially create the torque the factory forgot.
- Dual-Map Tuning: Optimizing ignition curves for the new PV engine.
- Transfer Port Hooking: Directing fuel charge away from the exhaust for efficiency.
- Transmission Tumbling: Critical for the YZ85's notoriously notchy gearbox.
The YZ125 is the best handling bike in the world, but stock-for-stock, it surrenders 3-4 horsepower to the Austrians. That ends here. Whether you have the new 2022+ engine (Keihin carb) or the previous generation, our goal is cylinder efficiency. We correct the factory 'short side radius' in the exhaust port to let the engine breathe past 11,000 RPM, giving you the power to pull 3rd gear in corners where you used to downshift to 2nd.
- Short Side Radius Correction: The secret to YZ125 over-rev.
- Combustion Chamber Shaping: Optimized for pump gas (93) or VP C12.
- Carb Boring: Expanding the venturi for maximum top-end airflow.
The YZ250 is a legend, but it has a dirty secret: a terrible factory squish clearance. Most stock YZ250s have a gap of over 1.8mm, leading to inefficient combustion and the infamous 'Yamaha Ping' (detonation) on pump gas. Our #1 priority with the YZ250 is cutting the head to correct the squish band to a tight 1.0mm-1.2mm. This eliminates detonation, sharpens throttle response, and allows the engine to run cooler and harder.
- The 'Squish Fix': Eliminating detonation risks on pump gas.
- X-Model Mapping: Custom CDI profiles for off-road traction.
- Linear Power Porting: Smoothing the violent mid-range hit for better control.
Common YZ Performance Questions
How do I fix the 'YZ bog' on my 125?
Jetting + Port Timing.
The infamous YZ125 bog is often a combination of rich factory jetting and conservative slide cutaways. Our engine packages address this by optimizing the transfer port signal strength and providing specific jetting baselines that clean up the transition from pilot to main jet.
Does the YZ250 need head work for pump gas?
Yes.
The stock YZ250 squish clearance is notoriously loose (often >1.8mm), which promotes detonation ('pinging') on modern pump gas. Our head re-profiling service corrects this to a safe 1.2mm, eliminating pinging while increasing torque.