KTM 640 LC4 Enduro (1998–2006): The Uncompromising Austrian Thumper

Overview

The KTM 640 LC4 Enduro is a motorcycle that refuses to be pigeonholed. Built during an era when dual-sport bikes were either street-biased compromises or dirt-focused bruisers, this Austrian machine carved its own path. From 1998 to 2006, it dominated conversations among riders who demanded a true "do-it-all" bike—one that could tear through singletrack trails, carve twisty tarmac, and even handle multi-day adventures. With its liquid-cooled 625cc single-cylinder engine, rally-bred chassis, and KTM’s signature orange aggression, the LC4 Enduro remains a benchmark for raw, unfiltered motorcycling. Let’s dissect why this bike still commands respect—and occasional fear—among enthusiasts.

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Engine and Performance: The Heart of a Lion

Power Delivery

At its core lies the 625cc (38.1 cu in) LC4 engine, a liquid-cooled single-cylinder powerplant producing 54 HP (40 kW) at 7,000 RPM and a stump-pulling 55 Nm (40.6 lb-ft) of torque at 5,500 RPM. This isn’t a polite thumper—it’s a snarling beast that demands respect. The Mikuni BST 40 carburetor (a constant across all model years) delivers a punchy, immediate throttle response, while the Kokusan ignition system ensures reliability even when submerged in mud or dust.

The LC4’s powerband is deceptive. Below 4,000 RPM, it chugs along like a tractor, ideal for crawling over rocks or navigating technical terrain. Crack the throttle past halfway, though, and the bike transforms into a snarling missile. Riders report a “light switch” effect at 5,500 RPM, where the engine hurls itself toward its 168 km/h (104 mph) top speed with single-minded urgency.

Vibration: The LC4’s Signature

Let’s address the elephant in the room: vibration. The LC4’s single-cylinder design and high-compression ratio (11.5:1) create a buzzing symphony that resonates through the handlebars, footpegs, and seat. At idle, it rattles fillings; at highway speeds, it turns hands into numb clubs. Yet, there’s a perverse charm to this character. As one owner noted: “After 10,000 km, either the bike smooths out or you go deaf. Either way, it stops bothering you.”

Counterbalancers introduced in later models (post-2002) reduced high-frequency vibes, but the LC4 remains a bike that communicates through its handlebars—for better or worse.

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On-Road vs. Off-Road: A Dual Personality

Tarmac Manners

With a 1510 mm (59.4 in) wheelbase and a steep 62° steering head angle, the LC4 feels surprisingly nimble on pavement. The 21-inch front wheel and long-travel WP USD 4357 MXMA forks (280 mm / 11 in of travel) lack the precision of a sportbike but reward aggressive riders with tenacious grip. The Brembo 4-piston caliper biting a 300 mm front disc delivers stoppies on demand, though the semi-knobby tires (90/90-21 front, 140/80-18 rear) howl in protest during hard cornering.

At 145–158 kg (320–348 lbs) wet, the LC4 is no featherweight, but its mass centralization makes it flickable. Owners praise its ability to transition from highway cruising to backroad scratching without missing a beat—though wind protection is nonexistent, and the seat feels like a 2x4 after 200 km.

Off-Road Dominance

Here’s where the LC4 shines. The WP suspension—43 mm USD forks up front and a Pro-Lever-linked shock out back—soaks up whoops, roots, and rocks with rally-bred composure. Ground clearance (310 mm / 12.2 in) lets you straddle logs, while the torquey engine powers up hillsides with minimal clutch work. The catch? That 12-liter (3.2 US gal) fuel tank limits range to ~200 km (124 miles) off-road, necessitating careful route planning or auxiliary tanks for serious adventuring.

The LC4’s weight becomes apparent in tight singletrack, where it’s less agile than smaller enduros. Yet, for riders who value torque over finesse, it’s a brute-force tool that laughs at obstacles.

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Competition: How the LC4 Stacks Up

Honda XR650L

The XR650L is the LC4’s polar opposite: air-cooled, softly tuned, and built for reliability over performance. While the Honda’s 644cc engine produces a modest 43 HP, it’s butter-smooth and virtually indestructible. The XR650L also boasts a larger 12.8-liter (3.4 US gal) tank and lower seat height (940 mm / 37 in vs. the KTM’s 930–955 mm / 36.6–37.6 in). However, its dated suspension and drum rear brake can’t match the KTM’s WP/Brembo package.

Verdict: Choose the Honda for low-maintenance commuting; the KTM for adrenaline-fueled versatility.

Suzuki DR650

Suzuki’s 644cc thumper splits the difference with a lower seat (885 mm / 34.8 in) and budget-friendly pricing. The DR650 is lighter (166 kg / 366 lbs) and smoother but lacks the KTM’s premium components. Its suspension is plush but undersprung for aggressive off-roading, and the 5-speed transmission feels agricultural compared to the LC4’s precise shifts.

Verdict: The DR650 is a better daily rider; the LC4 is the weekend warrior’s weapon.

Yamaha XT660Z Tenere

Yamaha’s 660cc single (48 HP) rivals the LC4 in power but wraps it in a more refined, ADV-focused package. The Tenere offers fuel injection, a 23-liter (6.1 US gal) tank, and adjustable windscreen—features the KTM lacks. However, at 189 kg (417 lbs), it’s a pig in technical terrain compared to the agile LC4.

Verdict: Tenere for transcontinental tours; LC4 for technical trails and raw thrills.

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Maintenance: Keeping the Beast Alive

The LC4 rewards diligent owners but punishes neglect. Here’s what to prioritize:

1. Oil Changes

• Frequency: Every 3,000–5,000 km (1,864–3,107 mi)
• Oil Type: 20W-60 full synthetic (2.1 liters / 2.2 qt with filter)
• Pro Tip: Use a magnetic drain plug to catch metal shavings from the high-strung engine.

2. Valve Adjustments

• Clearance: Intake/Exhaust: 0.12–0.15 mm (0.0047–0.0059 in) cold
• Tools Needed: Feeler gauge, 8 mm wrench
• Frequency: Every 10,000 km (6,214 mi)

3. Carburetor Tuning

The Mikuni BST 40 is reliable but finicky in extreme temps. Adjust the air screw (2.25 turns out stock) and consider a JD Jet Kit for altitude adjustments.

4. Chain and Sprockets

• Stock Gearing: 16/42 teeth
• Upgrade: Swap to a DID 520VX3 X-ring chain (5/8 x 1/4") and steel sprockets for longevity.

5. Suspension Service

• Fork Oil: SAE 5W (435–450 ml per leg)
• Rear Shock: Rebuild every 20,000 km (12,427 mi) with genuine WP seals.

MOTOPARTS.store Recommendations

• Air Filter: Twin Air foam filter for improved airflow and dirt protection.
• Seat Upgrade: KTM PowerParts Comfort Seat (adds 20 mm / 0.8 in padding).
• Handguards: Barkbusters Storm for crash protection.

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Verdict: The LC4’s Legacy

The KTM 640 LC4 Enduro isn’t for everyone. It vibrates like a paint shaker, guzzles fuel, and demands mechanical sympathy. But for riders who crave a visceral, unfiltered connection to the road—or trail—it’s a masterpiece. This is a bike that thrives on abuse, rewards skill, and laughs at modern electronics. As Clint from Kiwibiker famously said: “It’s the most versatile and funnest bike I’ve ever owned.”

Whether you’re chasing Dakar dreams or carving canyon roads, the LC4 remains a testament to KTM’s “Ready to Race” ethos. Just don’t forget your toolbox—and maybe a padded seat.

Looking to revitalize your LC4? Explore MOTOPARTS.store’s curated selection of performance upgrades, maintenance kits, and off-road accessories tailored for this iconic Austrian brute.

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Specifications sheet

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