How to Repair an Ignition in a Yamaha PW50

Written by brianna byrne
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How to Repair an Ignition in a Yamaha PW50
If the plug doesn't spark properly, the PW50's ignition system cannot work. (Stockbyte/Stockbyte/Getty Images)

The Yamaha PW50 dirt bike -- with a small 49cc engine -- is designed for children and young teenage riders. Despite its small size and engine, the PW50 is susceptible to the same mechanical problems as any vehicle. This is true of the PW50's ignition system. Yamaha recommends that owners attempt only minor repairs on the ignition system including diagnosis, replacement and adjustment of the dirt bike's spark plug. For major ignition system repairs, the company instructs owners to take the PW50 to a certified Yamaha dealer.

Skill level:

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Things you need

  • Spark plug wrench
  • Spark plug gap-tool
  • Wire thickness gauge
  • Shop rag
  • NGK BP4HS or DENSO W14FPL replacement spark plug

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  1. 1

    Locate the spark plug, situated inside the PW50 engine's single cylinder. Remove the spark plug cap to access the plug.

  2. 2

    Turn the spark plug counter-clockwise using a spark plug wrench. Remove it from the cylinder.

  3. 3

    Inspect the plug's porcelain insulator tip. This tip should appear light-brown or tan in colour. Replace it if its is blackened, white, brittle or damaged. The PW50 takes either an NGK BP4HS or a DENSO W14FPL spark plug.

  4. 4

    Measure the spark plug gap using a wire thickness gauge. For the PW50, the gap should be between 0.024 and 0.028 inches. This gap must be precise, as any alteration could be the source of ignition system problems.

  5. 5

    Shorten the spark plug gap by pressing the hook-end against a hard, flat surface until it reaches the necessary width.

  6. 6

    Widen the gap using a spark plug gap-tool. Pull the hook wider.

  7. 7

    Wipe the spark plug clean and dry. Reinsert it into the PW50 engine's cylinder, and twist it back into place with the spark plug wrench. Return the spark plug cap.

Tips and warnings

  • Use only the NGK BP4HS or DENSO W14FPL spark plug listed in the PW50's manual to avoid serious engine damage.

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