ATHENA Exhaust Power Valve Part for ATHENA cylinder kit for YAMAHA YZ 125 2022-2027

The ATHENA P400485303002 exhaust power valve part is designed for YAMAHA YZ 125 from 2022 to 2027. On a two-stroke motocross engine, the exhaust power valve changes the height of the exhaust port with the revs: low for mid-range torque, high for top-end power. Once it sticks or clogs up, it stops moving and the engine loses either its torque or its over-rev.

Specifications

• Brand: ATHENA
• Manufacturer part number: P400485303002
• EAN code: 8050506053781
• For ATHENA cylinder kit ref. P400485100101 (Ø58 mm)
• Weight: 140 g
• Engine: 2-stroke

When to replace it?

• Flat in the mid-range or running out of breath at high revs.
• Valve stuck with carbon, or slow to return to position.
• Excessive play, weak spring or marked parts on teardown.

Clean and check the power valve at every piston change, and replace worn parts as soon as they develop play or stop moving freely.

Fitting tips

1. Remove the power valve in the order given in the workshop manual and note the position of each part.
2. Decarbonise the valve housing in the cylinder before fitting the new parts.
3. Check that the valve slides freely over its full travel, with no tight spot, before closing up.
4. Adjust the valve (spring preload, stop) as set out in the manual, then reassemble with new gaskets.

Why ATHENA?

Athena, an Italian company founded in 1973 near Vicenza, designs gaskets, pistons and cylinder kits for motorcycles. An OEM supplier to KTM, Ducati, Fantic, Piaggio and Triumph and a partner of the MXGP world championship, it develops its parts on the test bench and on the track with racing teams.

Spare parts and items to plan

• ATHENA cylinder kit : ATHENA
• Piston : ATHENA
• Top end gasket kit : ATHENA
• Cylinder head and dome : ATHENA S410485308040 · ATHENA P400485200003
• Cylinder kit bolt kit : ATHENA

Frequently asked questions

Do I need to replace the whole valve?
No: replace the worn parts (blades, spring, shaft, seals) and check the others. Compare with the photo and your workshop manual.

Will this part fit my cylinder?
Check the compatibility list and the product name: some parts are made for the original cylinder, others for an Athena cylinder kit.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
YAMAHA YZ 125 2027
YAMAHA YZ 125 2026
YAMAHA YZ 125 2025
YAMAHA YZ 125 2024
YAMAHA YZ 125 2023
YAMAHA YZ 125 2022