How Can I Make My YZ125 Faster?

The Yamaha YZ125 is an off-road motorcycle that was first offered to consumers for the 1974 model year. With a 124 cubic-centimeter motor, current YZ125s feature 33 brake horsepower and 19 foot-pounds of torque. While this may seem like plenty of power to the average rider, you may seek to add a bit more get-up to your go. Simple bolt-on parts, such as the air filter and exhaust pipe, can greatly improve Yamaha's performance.

Things You'll Need

  • Performance air filter
  • Exhaust pipe
  • Spark plugs and wires
  • Socket wrench set
  • Flathead screwdriver
  • Philips-head screwdriver
  • Clean rag
  • Motorcycle stand
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Instructions

  1. Air Filter

    • 1

      Place the Yamaha on a stand to ensure it does not move during any of the maintenance procedures. Remove the seat of the dirt bike to access the air filter and surrounding parts.

    • 2

      Unfasten the hardware that holds the air filter to the throttle body of the engine to remove this piece from the bike. Slowly pull up on the filter, making sure that any debris does not fall back into the engine.

    • 3

      Spray the new, replacement filter with the oil that came with the air filter kit. This wire-mesh filter features a stronger and more resilient texture than factory models made out of paper. Clean this filter once it gets dirty, as it is completely re-usable.

    • 4

      Lower the new air filter into place, using the old hardware to fasten this piece to the throttle body. This filter should fit directly as the old one was before removal, therefore you must make sure that it fits snug into position.

    • 5

      Start your bike and make sure that no air is leaking near the connecting point of the filter and throttle body. Stop the engine and tighten the hardware if any leaks do occur. Replace the seat once you are confident in the installation of this filter.

    Exhaust Pipe and Manifold Gasket

    • 6

      Unscrew the bolts that hold the stock exhaust pipe to the engine, holding the pipe up as it still connects to the hanging hardware. Remove these screws that hold the exhaust pipe to the body and slide away carefully. Replacing your stock exhaust pipe with a performance model will increase air flow, which in turn increases power.

    • 7

      Remove the exhaust manifold gasket from the engine, as this piece separates the engine block from the exhaust pipe. After extended use, this gasket will become corroded and likely cause leaks if not replaced. Use a flat-head screwdriver to pry this piece away from the engine, if necessary.

    • 8

      Apply gasket sealant to the bottom of the new exhaust gasket. Align the new gasket over the engine block exactly as the old one was removed and wait ten minutes for the piece to bond.

    • 9

      Slide the new exhaust pipe into place, making sure that it aligns with the hanging hardware and the new exhaust manifold gasket. Hold the new pipe into place using the provided screws and the original hanging hardware of the YZ125.

    • 10

      Hand-screw the bolts of the exhaust pipe to the engine, making sure that it aligns with the new gasket. Torque the bolts to the necessary amount as stated in the new exhaust pipe owner's manual. Start your engine and make sure there are no leaks.