ATHENA Exhaust Power Valve Part for original and ATHENA cylinders for FANTIC XE 125, XX 125 and YAMAHA YZ 125 2022-2027

On FANTIC XE 125, XX 125 and YAMAHA YZ 125 from 2022 to 2027, the ATHENA P400485303001 exhaust power valve part fits in place of the original part. A two-stroke power valve works in hot exhaust gas and carbon. Over time it clogs up, develops play or sticks: the engine goes flat at the bottom or runs out of breath at the top.

Specifications

• Brand: ATHENA
• Manufacturer part number: P400485303001
• EAN code: 8050506053774
• For ATHENA cylinder kit ref. P400485100100 (Ø54 mm), P400485100102
• Weight: 100 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?

Founded in 1973 near Vicenza, Athena is an Italian engine gasket specialist that has made its gaskets on its own production lines since day one, as well as a renowned manufacturer of pistons and cylinder kits. The brand supplies original equipment to manufacturers such as KTM, Ducati, Fantic, Piaggio and Triumph, and is a partner of the MXGP motocross world championship.

Spare parts and items to plan

• ATHENA cylinder kit : ATHENA P400485100100 · ATHENA P400485100102
• Piston : ATHENA S4C05400024 · ATHENA S4C05400025
• Top end gasket kit : ATHENA
• Cylinder head and dome : ATHENA P400485200002 · ATHENA P400485200005 · ATHENA S410485308048
• 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:
FANTIC XE 125 2026
FANTIC XE 125 2025
FANTIC XE 125 2024
FANTIC XE 125 2023
FANTIC XX 125 2026
FANTIC XX 125 2025
FANTIC XX 125 2024
FANTIC XX 125 2023
FANTIC XX 125 2022
YAMAHA YZ 125 2027
YAMAHA YZ 125 2026
YAMAHA YZ 125 2025
YAMAHA YZ 125 2024
YAMAHA YZ 125 2023
YAMAHA YZ 125 2022