ATHENA Exhaust Power Valve Part for ATHENA cylinder kit for YAMAHA DT 125 1991-2004

The ATHENA S410485315001 exhaust power valve part is designed for YAMAHA DT 125 from 1991 to 2004. 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: S410485315001
• EAN code: 8051757097258
• For ATHENA cylinder kit ref. P400485100019 (Ø56 mm)
• Weight: 60 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
• Piston rings : ATHENA
• Top end gasket kit : ATHENA
• Cylinder head and dome : ATHENA S410485308004 · ATHENA S410485308005

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 DT 125 2004
YAMAHA DT 125 2003
YAMAHA DT 125 2002
YAMAHA DT 125 2001
YAMAHA DT 125 2000
YAMAHA DT 125 1999
YAMAHA DT 125 1998
YAMAHA DT 125 1997
YAMAHA DT 125 1996
YAMAHA DT 125 1995
YAMAHA DT 125 1994
YAMAHA DT 125 1993
YAMAHA DT 125 1992
YAMAHA DT 125 1991