Animated service guide
How to Check Two-Stroke Reed Valves
The reed valve is a one-way door between the carburetor or throttle body and the crankcase. The rising piston pulls the petals open and the mix rushes in. When the piston comes down the petals slam shut. A chipped, cracked or gapped petal leaks charge back out, and the bike starts harder and loses response. KTM checks the reed block every 15 hours on its SX and XC race two-strokes, and every 45 hours on the XC-W and EXC enduro bikes.
The animated guide loads here. Every step is also written out below.
Before You Start
Tools
- Hex keys and sockets
- Flashlight
- Small torque wrench (1 to 10 Nm)
- Gasket scraper (plastic)
Parts And Supplies
- Intake gasket or O-ring
- Replacement petals if any are damaged
- Carb or contact cleaner
Safety
- Turn the fuel off and drain the float bowl or relieve the fuel line before you pull the carb or throttle body.
- Cover the crankcase opening while the reed block is out.
Step By Step
Why the reeds matter
Watch the petals. They open only while the rising piston pulls a vacuum in the crankcase, then close as the piston comes down and pressurizes it. A petal that doesn’t seal lets that charge blow back out the intake. KTM lists a damaged reed or reed housing as a cause of lost power.
Reed check interval Bike Spec Source KTM / Husqvarna / GASGAS SX, XC, TC, MC, EX two-stroke (race) Every 15 h Check the reed valve housing, reed valve and intake flange. KTM 250/300 SX/XC 2024 OM PDF p. 36; KTM 250 SX 2022 OM PDF p. 34 KTM XC-W, EXC, Husqvarna TE 250 / 300 (enduro) Every 45 h Check the reed valve housing, diaphragm and intake manifold. KTM 2026 XC-W OM PDF p. 55; Husqvarna TE 250/300 2026 OM PDF p. 55 Check your manual. Many race two-stroke schedules check the reed block with the top end.
Get to the reed block
Turn the fuel off and pull the carburetor or throttle body back out of the intake boot. Remove the intake flange screws and lift the flange off. The reed block comes out behind it with its gasket. Stuff a clean rag in the crankcase opening.
- Hex key
- Rag
Light test the petals
Hold the reed block up to a bright light and look through it from the crankcase side. A good petal sits flat on its seat with no light around it. Light at the tip means a gap. Look for chips, cracks, frayed fiber and petals that stay lifted. Replace any petal that fails.
- Flashlight
Careful. A chipped petal can let pieces go into the engine. Don’t ride on one.
Check stoppers and screws
The stopper plates limit how far the petals open. They should be straight and evenly shaped on both sides, never bent flat or kinked. Make sure the petal screws are tight and the petals sit centered over their windows.
- Small torque wrench
Reed petal screws Bike Spec Source KTM / Husqvarna / GASGAS 250/300 1 Nm (0.7 lbf ft) Screws for the inner and outer membrane sheets and support plate. KTM 250/300 SX/XC 2024 OM PDF p. 133 Reed screws are tiny. Snug them gently or use the value in your manual. Overtightening cracks the petal or strips the cage.
Careful. These screws take very little torque. On KTM it is 1 Nm, about a firm twist of a small hex key.
Check the seat and gasket
Look at the rubber seat around each window. It should be bonded to the cage with no tears or lifted edges. Clean the flange faces and fit a new gasket. A torn gasket or flange crack lets in false air, which KTM lists as a cause of the engine dying.
- Plastic scraper
- Cleaner
Refit and torque
Fit the reed block with a new gasket, petals facing into the crankcase. Torque the flange screws evenly, refit the carb or throttle body and tighten its clamps. Start it and listen for a whistle or a hanging idle, which point at an air leak.
- Torque wrench
Intake flange / reed housing screws Bike Spec Source KTM / Husqvarna / GASGAS 250/300 6 Nm (4.4 lbf ft) M6 screw, intake flange/reed valve housing. KTM 250/300 SX/XC 2024 OM PDF p. 133; KTM 250 SX 2022 OM PDF p. 120 Use the intake flange torque from your manual.
Sources
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