GAS GAS Supermoto EC 125 / 200 / 250 / 300 Service Manual, 2003 (P/N PU010338018)

• Covers all 2003 GAS GAS EC liquid-cooled 2-stroke models: 125cc, 200cc, 250cc, and 300cc
• Official 58-page GAS GAS factory service manual dated February 2003
• Manufacturer publication P/N PU010338018
• Model-specific information separates the EC 125 from the EC 200/250/300 where different settings, illustrations, or service data apply

Engine & Drivetrain Specifications

This OEM manual delivers the technical data and maintenance schedules used for the 2003 GAS GAS EC 125, 200, 250, and 300 enduro models. Engine specifications identify each bore, stroke, and displacement, from the 54 x 54.5 mm / 124cc EC 125 through the 72 x 72 mm / 294.7cc EC 300. All four use liquid-cooled, crankcase-induction 2-stroke engines, a KEIHIN PWK 38 carburetor, CDI ignition, and 50:1 (2%) fuel/oil premix.

Drivetrain data goes well beyond a basic maintenance booklet. The publication lists all six transmission ratios, a 2.85 primary reduction ratio, 3.692 final reduction ratio, and 8.149 overall ratio in sixth gear. Ignition timing is specified as 1 mm APMS, while the tuning section explains how stator position affects ignition timing and power delivery. Fuel requirements, spark plug inspection, transmission lubrication, clutch adjustment, silencer packing, and drive-chain service are covered with factory reference values for repair planning.

Relevant factory procedures include ignition-timing inspection and adjustment, cooling-system draining and refilling, transmission-oil service, air-filter servicing, throttle free-play and carburetor idle adjustment, hydraulic clutch lever adjustment, silencer repacking, drive-chain slack and wheel alignment, steering-bearing adjustment, and competition preparation checks. The race-based Maintenance and Adjustment chart also covers piston and ring inspection, crankshaft and engine-bearing checks, brake service, suspension linkage, wheel bearings, steering bearings, fork oil, and rear-shock service intervals.

The torque information includes repair-critical values such as the 98 Nm rear axle nut, 27 Nm spark plug, 9 Nm water-pump cover drain plug, and 29 Nm fork top cap. A dedicated Torque Table covers engine, brake, axle, steering, suspension, and chassis fasteners rather than leaving these values scattered through the text.

Chassis, Suspension & Safety Data

Chassis specifications identify the chromoly tubular semi-double-cradle frame, 21-inch front and 18-inch rear wheel sizes, 260 mm front and 220 mm rear brake discs, 282 mm front suspension travel, and 320 mm rear travel. Brake service data specifies DOT 3 or DOT 4 fluid and a 1 mm minimum brake-pad thickness before pad replacement.

Suspension coverage is unusually detailed for a manual of this size. Front-fork specifications include 43 mm WP and 45 mm Marzocchi configurations, with the manual also providing Öhlins fork-oil data. Standard oil levels are 110 mm for Marzocchi, 120 mm for WP, and 110 mm for Öhlins, measured with the fork compressed and spring removed. Recommended oils are Marzocchi SAE 7.5, WP SAE 5, and Öhlins SAE 5–7.5.

The front fork has a 16-click rebound adjustment range, with 6–8 clicks out from fully hard listed as the standard setting. Fork-oil level, spring selection, fork-tube height, rebound, and compression settings are tied directly to rider weight and track conditions. Rear suspension coverage includes the linkage-type single shock, spring preload, spring replacement, and separate 60-click rebound and compression ranges; the standard settings are 25 clicks for rebound and 30 clicks for compression from fully closed.

Drive-chain specifications include 30–50 mm slack at the specified swingarm location and a 2% elongation wear limit. The manual also covers sprocket wear, chain-guide and slider inspection, master-link orientation, spoke and rim checks, tire bead locks, steering play, and wheel alignment.

Because fork, steering, brake, wheel, and rear-shock work directly affects motorcycle control, support the bike securely on a proper stand and use the manual's specified inspection and torque values before riding.

Carburetor, Suspension Tuning & Troubleshooting

The carburetor section is particularly useful for riders setting up the EC for changing temperature, altitude, and course conditions. It explains the working ranges of the main jet, slow/pilot jet, jet needle, needle-clip position, and air screw rather than providing only a stock jetting number.

For unleaded fuel, the standard-setting table lists a No. 7 throttle-valve cutaway, No. 38 slow jet, N1EC needle, and No. 185 main jet. The manual then uses an altitude/temperature correction-factor graph and a Jet Needle/Air Screw Chart to relate atmospheric changes to jetting and needle adjustments.

Suspension tuning receives similar treatment. Symptom-based sections address forks that feel too hard or soft, excessive brake dive, front-end push or oversteer, rear-end kick over braking bumps, poor rear traction, and front/rear bottoming. This gives technicians and experienced DIY riders diagnostic context before changing spring, oil-level, preload, rebound, or compression settings.

Useful charts and views include the Maintenance and Adjustment chart, Torque Table, component-location views, altitude/temperature Correction Factor chart, Jet Needle/Air Screw Chart, and multi-page troubleshooting cause/remedy tables. The troubleshooting section covers starting problems, overheating, loss of full power, abnormal engine noise, clutch slip or drag, jumping out of gear, steering and suspension complaints, brake faults, and drivetrain noise. GAS GAS speedometer instructions are also included for the clock, trip display, km/h or mph selection, backlight wiring, and 21-inch enduro / 17-inch supermoto wheel settings.

Repair-Specific Notes and Manual Scope

Several factory cautions are worth knowing before repair work begins. High-pressure washing can damage radiator fins and reduce cooling efficiency. Incorrect coolant or hard water can promote corrosion and scale buildup that damages the engine and cooling passages. The drive-chain master-link clip must be installed with its closed end facing the direction of chain rotation to reduce the risk of the link coming apart.

This factory publication is strongest on scheduled service, adjustment, setup, tuning, inspection, fault finding, and selected repair-level procedures. It is not laid out as a full internal engine-and-transmission teardown and overhaul manual, making that scope distinction important for buyers expecting complete crankcase, gearbox, or bottom-end rebuilding instructions.

The supplied PDF preserves the factory specifications, charts, component photographs, adjustment references, maintenance schedules, troubleshooting tables, and model-specific service information in one 2003 EC publication.