Yamaha's YZ125 is one of the smallest competition dirt bikes, but don't let size fool you. The 124cc two-stroke motor is capable of mind-numbing performance and is able to hold its own on the dirt track or the trail. But how do you keep this pocket rocket happy when you're not riding? Fortunately, two-stroke dirt bikes, like the little YZ, require very little maintenance and can provide years of enjoyment as long as you follow a basic maintenance schedule.
Use fresh fuel. Gasoline has a tendency to deteriorate over time, which can clog the carburettor's fuel jetting as the gas breaks down into sludge. Always ensure that the tank is filled with fresh gas before riding and storing.
Pre-mix the fuel with oil properly. Yamaha and most manufacturers recommend using a ratio of 32:1, or 118ml of oil to 1 gallon of gas. YZ125's that are used frequently for racing may benefit from a slightly richer 20:1 ratio, or 1814gr of oil to 1 gallon of gas
Replace your transmission oil once for every 20 hours of riding.
Check your spark plugs every 20 riding hours. Look for "fouling," or oily, black build-up on the electrode end of the spark plug. Fouled plugs are often a sign of mechanical failure somewhere in the motor.
Inspect your air filter often. Dirty air filters starve the motor of air and create a loss of power. Stock paper air filters turn black as they get dirty and will need replacement. Alternatively, aftermarket foam air filters can usually be cleaned and re-oiled.
Check your front suspension for leaks. Clean the fork tubes, then--while pulling in the front brake lever--press down on the front end to compress the forks. Release the brake as the forks extend and run your finger along the fork tube. If your finger comes away coated with fork oil, you may have a leaking fork seal, which will need replacement before riding.
Flush and bleed the brake systems. Dirty brake fluid and air bubbles in the brake lines will cause a loss of braking ability, most often displayed as a soft, mushy-feeling brake lever. Replacing the fluid and bleeding the air from the brake lines can restore and even enhance brake performance and feedback.
Check your wheels for broken or bent spokes and replace any that are damaged. Also, check your rims for dents. Your wheels are all that separate you from the ground and any defects can cause a loss of control.
Check your tires for tread wear and punctures. If the tread is worn out or uneven, replace the tire. Likewise, any holes or punctures in the rubber may mean that the inner tube is compromised, as well. Replace the tube before riding again.
Clean your YZ125. Besides the fact that a clean bike is a healthy bike, any oil leaks or damage that would otherwise be concealed by dirt will be visible. Always clean your bike after every ride.
Invest in a service manual for your bike. These manuals are available from your local Yamaha dealer and are filled with the technical details required to fully maintain your YZ125. If you experience a problem that is beyond your technical skills, take your YZ125 to a qualified Yamaha technician.
Do not ride your YZ125 if you suspect that the front fork seals are leaking. Fork fluid is extremely slick and may interfere with the front brake or tyre's ability to grip properly. Replace the fork seal immediately or consult a qualified Yamaha technician. If your YZ125 consistently fouls spark plugs, you may have damage within the motor. Stop riding your YZ125 immediately and consult a qualified Yamaha technician.