KTM 125 SX 2019 User Manual (English)

Questions and Answers:

A
Ashley NelsonJul 29, 2025
Why is my KTM 125 SX 2019 Motorcycle engine overheating?
- C
  Christina MendozaJul 30, 2025
  Your KTM Motorcycle engine might be overheating due to several reasons. It could be due to too little coolant in the cooling system, so you should check the cooling system for leakage and the coolant level. Another cause could be too little air stream, in which case you should switch off the engine when stationary. Also, check if the radiator fins are very dirty and clean them if needed. Other potential causes include foam formation in the cooling system (drain and refill the coolant), a damaged cylinder head or cylinder head gasket (check them), or a bent radiator hose (replace it).
V
Victor LopezAug 5, 2025
What to do if my KTM 125 SX 2019 engine stalls or pops into the carburetor?
- J
  Jacob HensleyAug 6, 2025
  If your KTM Motorcycle engine stalls or pops into the carburetor, it might be because the engine is taking in bad air. Check the intake flange and carburetor for tightness. Another possible cause is a loose or oxidized connector or ignition coil; in this case, clean the connector and treat it with contact spray.
J
Jimmy BallardAug 13, 2025
Why does my KTM Motorcycle emit white smoke from the exhaust?
- J
  jennifer68Aug 14, 2025
  If your KTM Motorcycle emits white smoke (steam) in the exhaust gas, it may be due to a damaged cylinder head or cylinder head gasket. You should check the cylinder head and cylinder head gasket.
T
Thomas AliAug 21, 2025
Why is gear oil coming out of the vent hose on my KTM Motorcycle?
- M
  Megan MeyerAug 21, 2025
  If gear oil is exiting at the vent hose of your KTM Motorcycle, it's likely because too much gear oil was added. Check the gear oil level.

KTM 125 SX 2019 Specifications

General

Displacement	124.8 cm³
Starter	Kickstarter
Transmission	6-speed
Fuel System	Mikuni TMX 38
Front Brake	Disc brake
Rear Brake	Disc brake
Ground Clearance	375 mm
Seat Height	950 mm
EMS	Kokusan
Engine Type	1-cylinder, 2-stroke
Bore x Stroke	54 mm x 54.5 mm
Rear Suspension	WP shock absorber with linkage
Fuel Tank Capacity	7.5 l
Clutch	Wet, multi-disc clutch, Brembo hydraulics
Frame Design	Central tube frame made of chrome molybdenum steel

Summary

Means of Representation

Symbols Used in the Manual

Explains the meaning of various symbols used in the manual.

Formats Used in the Manual

Details the typographical conventions applied throughout the document.

Safety Advice and Warnings

Intended Use, Misuse, and General Safety

Defines proper vehicle usage and general safety guidelines.

Risk Degrees, Safe Operation, and Tampering Warnings

Outlines danger levels, safe operating practices, and warnings against tampering.

Protective Clothing and Work Rules

Specifies required protective gear and rules for performing work on the vehicle.

Owner's Manual and Environmental Protection

Addresses environmental responsibility and the importance of the owner's manual.

Important Notes for Owners

Warranty, Service, and Customer Support

Covers warranty conditions and the importance of adhering to the service schedule.

Spare Parts and Operating Substances

Information on approved parts, fluids, and how to get customer support.

View of Vehicle Components

Motorcycle Front and Rear Views

Illustrates the motorcycle's front and rear views with labeled components.

Serial Numbers Identification

Locating Vehicle Identification Numbers

Details where to find the chassis, engine, type label, and part numbers.

Motorcycle Controls Overview

Handlebar Controls (Levers, Grips, Switches)

Explains the function and location of clutch, brake levers, and throttle grip.

Engine and Transmission Controls

Details the kill switch, choke, shift lever, and kick starter operations.

Fuel and Parking Controls

Covers the fuel tap, filler cap, foot brake, and plug-in stand functions.

Preparing the Motorcycle for Use

First Use Advice and Engine Break-in

Guidance for initial operation and engine running-in procedures.

Adapting for Difficult Riding Conditions

Instructions for preparing the vehicle for various challenging terrains and conditions.

Riding Instructions and Procedures

Pre-Ride Checks and Starting the Engine

Essential checks before riding and how to start the engine safely.

Riding Techniques and Brake Application

Advice on shifting, acceleration, deceleration, and proper braking.

Stopping, Parking, and Transporting the Vehicle

Guidelines for safely stopping, parking, and transporting the motorcycle.

Service Schedule

Required and Recommended Maintenance Intervals

Outlines the schedule for essential maintenance tasks and checks.

Tuning the Chassis

Basic Chassis Setup and Suspension Principles

Explains how to set up the chassis based on rider weight and general suspension principles.

Fork Adjustment Procedures

Step-by-step guide for adjusting fork air pressure, compression, and rebound damping.

Shock Absorber Adjustment Procedures

Detailed instructions for adjusting compression, rebound damping, and spring preload.

Handlebar Position Adjustment

Instructions on how to adjust the handlebar position for rider comfort.

Service Work on the Chassis

Fork and Steering Head Maintenance

Procedures for removing, installing, cleaning, and adjusting fork and steering head components.

Frame and Bodywork Maintenance

Covers removal and installation of fenders, seats, air filter box, and silencer.

Clutch and Brake System Service

Details on adjusting clutch lever, checking/changing hydraulic clutch fluid.

Brake System Maintenance

Hand Brake System Checks and Adjustments

Procedures for checking and adjusting hand brake lever free travel and position.

Front Brake Fluid and Linings Maintenance

Covers checking/adding front brake fluid and inspecting/changing brake linings.

Rear Brake System Checks and Adjustments

Details on checking/adjusting foot brake lever and servicing rear brake fluid and linings.

Wheels and Tires

Front and Rear Wheel Removal and Installation

Step-by-step guide for removing and installing both front and rear wheels.

Tire Condition and Pressure Checks

How to inspect tires for wear and damage, and check/correct air pressure.

Spoke Tension Check and Adjustment

Procedure for checking and correcting spoke tension for wheel integrity.

Cooling System Management

Coolant Level and Radiator Cover Procedures

Instructions for checking coolant, installing radiator covers, and draining/refilling coolant.

Tuning the Engine

Throttle Cable and Carburetor Idle Adjustment

Procedures for checking and adjusting throttle cable play and idle speed.

Carburetor Jetting and Settings

Guidance on tuning the carburetor for optimal performance based on conditions.

Ignition Timing and Shift Lever Settings

Information on adjusting ignition timing maps and shift lever basic position.

Service Work on the Engine

Carburetor Float Chamber and Gear Oil Maintenance

Procedures for emptying carburetor float chamber and checking/changing gear oil.

Cleaning and Care

Motorcycle Cleaning Procedures and Best Practices

Guidelines for safely and effectively cleaning the motorcycle.

Storage Guidelines

Long-Term Storage Preparation and Post-Storage Checks

Steps for preparing the motorcycle for storage and getting it ready for use afterward.

Technical Data

Engine and Chassis Specifications

Key technical data for engine design, displacement, and chassis dimensions.

Carburetor Settings and Tuning Data

Detailed specifications for carburetor types, settings, and tuning parameters.

Fork, Shock Absorber, and Tire Specifications

Technical data for suspension components, fork settings, and tire specifications.

Chassis Tightening Torques

Torque values for various chassis fasteners to ensure proper assembly.

Substances and Fluids

Brake Fluid, Coolant, and Engine Oil Specifications

Details on required fluids, their classifications, and recommended suppliers.

Auxiliary Substances Guide

Recommended Lubricants, Cleaners, and Additives

List of recommended auxiliary substances for maintenance and care.

Standards and Classifications

Industry Standards for Fluids and Materials

Explanation of standards like JASO and SAE relevant to vehicle fluids.

List of Abbreviations

Glossary of Common Abbreviations

Definitions of abbreviations found throughout the document.

Related product manuals

KTM 125 SX 2019 User Manual

Table of Contents