DOMA Expansion Chamber for YAMAHA YZ 250 and FANTIC XX 250 2007-2026

The DOMA 100402 expansion chamber is designed for YAMAHA YZ 250 and FANTIC XX 250 from 2007 to 2026. On a two-stroke, the expansion chamber isn't just a pipe: its cones send back a pressure wave that fills the cylinder better at the right rpm. Its shape gives the engine its character, and a dented pipe costs power.

Key features

• Handmade in Calais, France.
• 1 mm raw steel, laser-cut parts, pressed and then welded on a jig.
• Developed on the dyno and on the track.
• Works with the stock silencer or a Doma silencer.

Specifications

• Brand: DOMA
• Manufacturer part number: 100402
• Engine: 2-stroke

Who is it for?

• Stock pipe dented or cracked after a crash.
• Looking for more response and more power.

Good to know

Competition use only: this pipe is not road-legal.

Fitting tips

1. Reuse the stock connecting O-rings if they're in good condition (not included), or fit a new exhaust gasket.
2. Offer up the pipe without forcing it, fit all the mounts, then tighten.
3. Warm up the engine and check for leaks at the joints.
4. Check the colour of the spark plug after the first few rides.

Why DOMA?

A French workshop based in Calais since 1992, Doma Racing designs and handbuilds two-stroke expansion chambers and silencers. A 125 world title in 2000 with Grant Langston and original equipment at KTM: a brand run by two-stroke enthusiasts.

Spare parts and items to plan

• Exhaust gasket : ATHENA · CENTAURO
• Spark plug : NGK 3430 · NGK 3130

Frequently asked questions

Do I need to change the silencer?
No: the pipe works with the stock silencer or a Doma silencer.

Is it road-legal?
No: for competition use on closed circuits only.

Compatibility

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

Fits:
FANTIC XX 250 2026
FANTIC XX 250 2025
FANTIC XX 250 2024
FANTIC XX 250 2023
FANTIC XX 250 2022
FANTIC XX 250 2021
YAMAHA YZ 250 2026
YAMAHA YZ 250 2025
YAMAHA YZ 250 2024
YAMAHA YZ 250 2023
YAMAHA YZ 250 2022
YAMAHA YZ 250 2021
YAMAHA YZ 250 2020
YAMAHA YZ 250 2019
YAMAHA YZ 250 2018
YAMAHA YZ 250 2017
YAMAHA YZ 250 2016
YAMAHA YZ 250 2015
YAMAHA YZ 250 2014
YAMAHA YZ 250 2013
YAMAHA YZ 250 2012
YAMAHA YZ 250 2011
YAMAHA YZ 250 2010
YAMAHA YZ 250 2009
YAMAHA YZ 250 2008
YAMAHA YZ 250 2007