KTM 250 SX (2003-2006): A Lightweight Legend of the Motocross World

Introduction

The early 2000s were a golden era for two-stroke motocross bikes, and the KTM 250 SX (2003-2006) stands out as one of the most memorable machines of its time. Designed for riders who crave explosive power and razor-sharp handling, this Austrian-built motocrosser carved its reputation as a competitive weapon on tracks worldwide. Let’s dive into what made this generation of the 250 SX a favorite among privateers and weekend warriors alike – and why it still holds up today.

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Engine Performance: Two-Stroke Fury

At the heart of the KTM 250 SX lies its 249cc liquid-cooled two-stroke engine, a powerplant that embodies the raw, unfiltered thrill of premix-powered motocross. The 66.4 mm bore and 72 mm stroke configuration delivers a visceral hit of torque that’s addictive from the moment you kickstart the bike (yes, it’s kick-only – no electric start here).

The Keihin PWK 36/38 AG carburetor (varies by model year) provides crisp throttle response, though it demands careful jetting for optimal performance in different climates. Riders will notice an aggressive mid-to-top-end powerband characteristic of competition-focused two-strokes. This isn’t a bike that coddles beginners – it rewards precise throttle control with arm-straightening acceleration that can still humble modern four-strokes in straight-line sprints.

A 5-speed transmission keeps the power usable, though most riders will live in 2nd-4th gears on technical tracks. The hydraulically operated wet multi-disc clutch deserves special praise – its light pull and consistent engagement make it easier to manage the engine’s explosive character during long motos.

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Chassis & Handling: Precision Meets Durability

KTM’s chromoly double-cradle frame (25 CrMo4) strikes an impressive balance between rigidity and flex. At 1,475 mm (58.1") wheelbase and 97.7 kg (215 lbs) dry weight, the 250 SX feels remarkably nimble – almost like a 125cc bike with grown-up power. The 24-27° rake (varies slightly by year) and 63-116 mm trail figures create steering that’s quick but not twitchy, inspiring confidence in rutted corners and high-speed sweepers alike.

Suspension is where this generation truly shines. The WP-USD 48 mm forks (300 mm/11.8" travel) and WP-PDS rear shock (335 mm/13.2" travel) were class-leading components in their era. While modern bikes have moved to linkage-type rear suspension, the PDS (Progressive Damping System) design offers simpler maintenance and surprisingly good bottoming resistance for aggressive riders.

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Ergonomics & Comfort

With a 925 mm (36.4") seat height, the KTM towers over some competitors – a blessing for taller riders but challenging for those under 175 cm (5'9"). The narrow chassis design helps compensate, allowing most riders to dab a foot when needed. Standing up reveals a natural rider triangle, with handlebars and pegs positioned for aggressive attack positions.

The 7.5L (1.98 gal) fuel tank limits range to about 45-60 minutes of hard riding – typical for motocrossers but worth noting for those considering hare scrambles.

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Braking & Wheels

Front (260 mm) and rear (220 mm) single discs with hydraulic calipers provide ample stopping power for a bike this light. The initial bite is less aggressive than Japanese competitors, offering better modulation in slick conditions.

Spoked wheels with 21" front and 19" rear diameters wrapped in 80/100-21 and 110/90-19 tires (respectively) remain the MX standard. The ground clearance of 385 mm (15.2") helps avoid casing on big jumps or deep ruts.

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Competition: How It Stacks Up

The 2003-2006 KTM 250 SX faced fierce competition from:

1. Yamaha YZ250:
2. Similar power delivery but with a slightly broader powerband
3. Conventional rear suspension linkage vs KTM’s PDS

4. Heavier feel at 103 kg (227 lbs) dry

5. Honda CR250R:

6. More refined engine character but less peak power
7. Aluminum frame divided rider opinions on flex vs stiffness

8. Generally more expensive to maintain

9. Suzuki RM250:

10. Sharpest steering in class
11. Softer suspension stock-for-stock
12. Less durable transmission components

Where the KTM excelled was in its power-to-weight ratio and suspension performance. While Japanese bikes often required immediate aftermarket upgrades, the 250 SX could compete at club levels right off the showroom floor.

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Maintenance: Keeping the Orange Beast Alive

As MOTOPARTS.store journalists, we’ve seen these bikes age gracefully – provided owners address these key areas:

Engine Longevity

• Premix Ratio: Stick to 1:60 (1.67%) with quality synthetic oil
• Piston Replacement: Every 40-50 hours for aggressive riders
• Cooling System: Flush annually – these liquid-cooled engines run hot in slow trails

Suspension TLC

• Fork Seals: Upgrade to SKF seals for longer life
• PDS Shock: Rebuild every 100 hours – watch for nitrogen pressure loss
• Linkage Bearings: Not applicable (PDS system), but check swingarm pivots

Common Upgrades

1. Carburetor: JD Jet Kit solves altitude/temperature fussiness
2. Grips: ODI lock-ons reduce vibration fatigue
3. Brake Pads: Sintered metal compounds improve bite
4. Footpegs: Wider aftermarket pegs aid control

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Riding Impressions: A Time Machine with Teeth

Throwing a leg over a well-maintained 250 SX today is like uncorking a vintage wine – it reminds you why pure two-strokes remain irresistible. The engine’s hit is immediate but manageable, with a powerband that encourages aggressive clutch work. In tight corners, the bike flicks sideways with minimal input, while the suspension soaks up braking bumps that would deflect stiffer modern setups.

The lack of engine braking takes getting used to for four-stroke converts, but it becomes an advantage once mastered – carry more corner speed and brake later. On jump faces, the lightweight chassis makes mid-air corrections feel effortless.

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Conclusion: Why It Still Matters

The 2003-2006 KTM 250 SX represents the pinnacle of pre-TPI two-stroke development. While modern bikes offer more refinement, this generation delivers an undiluted riding experience that’s becoming increasingly rare. For riders who value mechanical simplicity, explosive power, and a direct connection to the track, few bikes deliver as much raw excitement per dollar – especially when maintained with quality aftermarket parts.

Ready to revitalize your KTM 250 SX? Explore MOTOPARTS.store’s curated selection of upgrade kits, OEM replacements, and performance accessories tailored for this iconic motocrosser. From WP suspension rebuild kits to carburetor jetting solutions, we’ve got everything to keep your orange machine dominating the track.

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Specifications sheet

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