GAS GAS MC 125 2021 - User Manual

Questions and Answers

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Danielle DudleyAug 18, 2025
Why does my GAS GAS Motorcycle engine have too little power?
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  Alison DawsonAug 18, 2025
  If your GAS GAS Motorcycle engine has too little power, first check for any interruptions in the fuel feed by inspecting the fuel tank breather, cleaning the fuel tap, and checking/setting the carburetor components. Clean the air filter and air filter box. Inspect the exhaust system for damage and replace the glass fiber yarn filling in the main silencer if needed. Check the ignition system for any faults. Lastly, examine the diaphragm and reed valve housing for any damage.
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Amanda SanchezAug 21, 2025
How to fix an overheating GAS GAS Motorcycle engine?
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  Claudia SilvaAug 21, 2025
  If your GAS GAS Motorcycle engine is overheating, start by checking the cooling system for leakage and ensuring the coolant level is correct. Make sure there is enough air stream and switch off the engine when stationary. Clean the radiator fins if they are very dirty. If there's foam formation in the cooling system, drain and refill the coolant. Also, inspect the cylinder head and cylinder head gasket for damage and replace any bent radiator hoses.
J
Jacob Martinez DDSAug 26, 2025
Why does my GAS GAS Motorcycle have no idle speed?
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  Scott LongAug 26, 2025
  If your GAS GAS Motorcycle engine has no idle speed, the idling jet might be blocked, so check and set the carburetor components. The adjusting screws on the carburetor might be distorted; in this case, adjust the idle speed. Replace the spark plug if it is defective. Also, check the ignition coil and the spark plug connector for any defects in the ignition system.
K
Kimberly GonzalezAug 28, 2025
What to do if my GAS GAS Motorcycle engine stalls or pops into the carburetor?
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  Heather NormanAug 28, 2025
  If your GAS GAS Motorcycle engine stalls or is popping into the carburetor, it could be due to a lack of fuel. Turn the knurled screw on the fuel tap all the way counterclockwise and refuel if necessary. Check the intake flange and carburetor for tightness to ensure the engine isn't taking in bad air. Also, clean any loose or oxidized connectors and treat them with contact spray.
T
Tammy PerrySep 1, 2025
Why does my GAS GAS Motorcycle engine not speed up?
- K
  Karla ThompsonSep 1, 2025
  If your GAS GAS Motorcycle engine does not speed up, it could be due to the carburetor running over because the float needle is dirty or worn, so check and set the carburetor components. Also, loose carburetor jets can cause this issue, so check and set the carburetor components. Finally, a fault in the ignition system can be the cause, so check the ignition system.
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Alyssa BrownSep 5, 2025
Why is my GAS GAS Motorcycle emitting white smoke?
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  Melvin StewartSep 5, 2025
  If you notice white smoke emission (steam in exhaust gas) from your GAS GAS Motorcycle, it could be due to a damaged cylinder head or cylinder head gasket. In this case, check the cylinder head and cylinder head gasket.
M
Matthew HughesSep 9, 2025
Why is gear oil coming out of the vent hose on my GAS GAS Motorcycle?
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  Luis KennedySep 9, 2025
  If gear oil exits at the vent hose of your GAS GAS Motorcycle, it is likely due to too much gear oil being added. Check the gear oil level to resolve this issue.
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Ashley HudsonNov 13, 2025
What to do if my GAS GAS Motorcycle engine turns but does not start?
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  Kara FarmerNov 13, 2025
  If your GAS GAS Motorcycle engine turns over but doesn't start, several factors could be at play. First, ensure you're following the correct start procedure. If the motorcycle has been sitting unused for a while, the old fuel in the float chamber might be the issue, in which case you should empty the carburetor float chamber. Check for any interruptions in the fuel feed by inspecting the fuel tank breather and cleaning the fuel tap. Also, check and adjust the carburetor components. If the spark plug is oily or wet, clean and dry it, or replace it if needed. Make sure the plug gap is correctly adjusted to 0.60 mm (0.0236 in). Inspect the ignition system, stop button, and wiring harness for any faults or frayed cables. Clean any loose or oxidized connectors and treat them with contact spray....

Summary

SAFETY ADVICE

Intended Use and Misuse

Defines proper use and outlines potential misuse scenarios.

Risk Degrees and Symbols

Identifies danger levels and associated symbols for safety.

Safe Operation Practices

Outlines safe riding, work rules, environmental awareness, and manual importance.

CONTROLS AND OPERATION

Component Identification

Illustrates and labels key components of the motorcycle.

Handlebar Controls

Describes clutch, brake levers, and throttle grip functions.

First Use Preparations

Key checks and adjustments before the first ride.

RIDING INSTRUCTIONS

Pre-Ride Checks

Essential checks before every trip to ensure safe operation.

Starting, Shifting, and Braking

Procedures for starting, shifting gears, and applying brakes.

Parking and Transporting

Safe methods for stopping, parking, and transporting the motorcycle.

CHASSIS TUNING AND SERVICE

Suspension Settings

Adjusting chassis, fork, and shock absorber settings for rider and conditions.

Chain and Wheel Service

Maintenance procedures for the drive chain and wheels.

Chassis Component Service

Procedures for servicing fork legs, triple clamps, and related chassis parts.

BRAKE, WHEEL, AND COOLING SYSTEMS

Brake System Maintenance

Checking and adjusting brake levers, fluid levels, and linings.

Wheel and Tire Service

Procedures for removing, installing, and checking wheels and tires.

Cooling System Maintenance

Checking and maintaining the cooling system, including coolant and radiator.

ENGINE TUNING AND SERVICE

Carburetor and Throttle Tuning

Adjusting carburetor settings and throttle cable play for optimal performance.

Gear Oil Maintenance

Checking, changing, and adding gear oil for transmission lubrication.

TROUBLESHOOTING

Engine and Electrical Faults

Diagnosing and resolving common engine and ignition system issues.

Cooling and Emission Faults

Troubleshooting engine overheating, smoke, and coolant leaks.

TECHNICAL DATA

Engine and Carburetor Specifications

Key engine dimensions, specifications, and carburetor settings.

Torque Values

Critical torque values for various screws and nuts on the chassis and engine.

GAS GAS MC 125 2021 Specifications

General

Displacement	124.8 cm³
Bore x Stroke	54 mm x 54.5 mm
Transmission	6-speed
Seat Height	950 mm
Front Brake	Disc brake
Rear Brake	Disc brake
Starter	Kickstarter
Compression Ratio	12.5:1
Engine Type	Single-cylinder, 2-stroke
Rear Suspension	Monoshock
Clutch	Wet multi-disc
Frame	Steel
Fuel Tank Capacity (approx.)	7.5 liters
Front Wheel	21 inches
Dry Weight	78 kg (172 lbs)
Fuel Tank Capacity	7.5 liters