GAS GAS MC 125 [2021-2023]: A Purebred Motocross Machine Tested

Introduction

The GAS GAS MC 125 is a motorcycle that demands attention in the 125cc motocross segment. Born from Spanish off-road heritage and now infused with modern Austrian engineering DNA (thanks to its KTM Group ownership), this two-stroke machine is designed for riders who crave agility, raw power-to-weight ratios, and track-ready performance. After spending a day throwing it around a motocross circuit, it’s clear this bike isn’t just a starter machine—it’s a serious tool for honing skills and chasing podiums.

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Engine Performance: Two-Stroke Thrills Refined

At the heart of the MC 125 lies a 124.8cc single-cylinder two-stroke engine, producing 40 HP (29.2 kW). For a small-displacement bike, these numbers are staggering—especially when paired with its featherweight 87.5 kg (193 lbs) dry weight. The result? A 0.457 HP/kg power-to-weight ratio that rivals larger machines.

The Mikuni TMX carburetor delivers crisp throttle response, with a hit of power that feels like a switchblade snapping open. Unlike older two-strokes that demand constant clutch work, the MC 125’s powerband is surprisingly manageable. Below 7,000 RPM, it chugs along politely, but once the revs climb, the bike transforms into a snarling beast. The 6-speed gearbox is slick, though I found myself rarely using 6th gear on tighter tracks—it’s better suited for longer straights or open terrain.

Key Takeaway: This engine rewards aggressive riders but doesn’t punish beginners. The Brembo hydraulic clutch ensures smooth modulation, crucial for managing that explosive top-end rush.

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Chassis and Handling: Precision Meets Durability

The MC 125’s 25CrMo4 steel double-cradle frame strikes a balance between flex and rigidity. On choppy terrain, the chassis absorbs impacts without feeling vague, while cornering precision remains razor-sharp. With a 1,475 mm (58.1") wheelbase and 26.1° rake angle, it’s flickable enough to carve inside lines but stable at speed.

Suspension Setup:
- Front: WP XACT-USD 48 mm forks with 310 mm (12.2") travel
- Rear: WP XACT Monoshock with 300 mm (11.8") travel

The WP suspension is sublime. Even at stock settings, it handles everything from hardpack jumps to deep ruts. I bottomed out once on a poorly timed landing, but tweaking the preload would easily solve this. The 950 mm (37.4") seat height is tall—ideal for stand-up riding but challenging for shorter riders. Consider a lowering link or seat shaving if you’re under 175 cm (5'9").

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Ergonomics and Ride Feel

GAS GAS sticks to a minimalist approach. The narrow bodywork lets you grip the bike with your knees effortlessly, and the handlebar positioning encourages an aggressive forward stance. After two hours of riding, fatigue set in—not from vibration (which is minimal for a two-stroke) but from the sheer physicality of controlling this lightweight rocket.

The 7-liter (1.85-gallon) fuel tank is adequate for 30-45 minutes of hard riding. For all-day practices, plan on refueling breaks or invest in a larger aftermarket tank from MOTOPARTS.store.

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Competition: How It Stacks Up

The 125cc motocross class is fiercely competitive. Here’s how the MC 125 compares:

1. KTM 125 SX
2. Shares the same engine and WP suspension but with different mapping.
3. KTM feels slightly more aggressive in mid-range power delivery.

4. GAS GAS edges ahead in cornering stability due to subtle frame geometry differences.

5. Yamaha YZ125

6. Yamaha’s liquid-cooled two-stroke is legendary for reliability.
7. MC 125 has superior suspension and a 3.5 kg (7.7 lbs) weight advantage.

8. YZ125’s carburetor lacks the Mikuni TMX’s crispness.

9. Husqvarna TC 125

10. Nearly identical to the GAS GAS but with a composite subframe.
11. Husky’s Magura clutch vs. GAS GAS’s Brembo—preference depends on lever feel.

Verdict: The MC 125 sits between the KTM’s rawness and Husqvarna’s refinement, offering a unique blend of Spanish flair and Austrian tech.

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Maintenance: Keeping the Beast Alive

Two-strokes are simpler than four-strokes, but the MC 125 still demands attention:

1. Top-End Rebuilds
2. Expect to rebuild the piston every 30-40 hours for competitive riders.

3. MOTOPARTS.store stocks OEM-sized pistons and gasket kits.

4. Carburetor Tuning

5. The Mikuni TMX is tunable but sensitive to altitude/temperature changes.

6. Keep spare jets and a carb rebuild kit in your toolbox.

7. Suspension Servicing

8. WP forks need oil changes every 50 hours. Use 5W oil for most conditions.

9. Chain and Sprockets

10. The 520 chain wears quickly under hard use. Upgrade to an O-ring chain for longevity.

11. Cooling System

12. Flush coolant annually. Use a 50/50 mix of ethylene glycol and distilled water.

Pro Tip: Always check the NGK BR9ECMIX spark plug gap after muddy rides—carbon buildup is common in two-strokes.

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Conclusion: Who Is It For?

The GAS GAS MC 125 is a riotous blend of old-school two-stroke character and modern engineering. It’s perfect for:
- Riders transitioning from 85cc machines
- Vet racers wanting a lightweight challenge
- Anyone who enjoys wrenching as much as riding

While it’s not the cheapest bike to maintain, its accessibility and sheer fun factor justify the effort. At MOTOPARTS.store, we’ve got your back with everything from performance pipes to grippy seat covers—because this bike deserves to stay on the track, not in the garage.

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Specifications sheet

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