The Yamaha PW50, a beloved first motorcycle for countless young riders, is known for its simplicity and reliability. However, even these pint-sized powerhouses can sometimes be stubborn when it comes to starting. A frustrating experience for both child and parent, a PW50 that refuses to fire up can quickly derail a fun day of riding. Understanding the common culprits behind these starting issues is the first step towards getting your little ripper back on the trail.

Why Won't My PW50 Start? Let's Play Detective!

Okay, so your PW50 is refusing to cooperate. Before you start tearing things apart, let's approach this systematically. Think of yourself as a motorcycle detective, hunting down clues to solve the mystery of the non-starting PW50. Here's a breakdown of the usual suspects:

  • Fuel Delivery Problems: This is often the most common cause. If the engine isn't getting fuel, it simply can't start.
  • Spark Issues: No spark, no bang. A weak or non-existent spark will prevent combustion.
  • Compression Troubles: The engine needs to compress the air/fuel mixture for proper ignition. Low compression means a weak or no start.
  • Air Intake Blockage: If the engine can't breathe, it can't run.
  • Electrical Gremlins: While less frequent on the PW50, electrical issues can still cause starting problems.

Let's dive deeper into each of these potential problems.

Fuel, Glorious Fuel! Is It Getting to the Engine?

Fuel delivery is the lifeline of any internal combustion engine. Here's what to check on your PW50:

  • Fuel Tank: Obvious, but crucial. Make sure there's actually fuel in the tank! Old fuel can also cause problems. Drain the tank and refill with fresh gasoline if the fuel has been sitting for a long time (especially over the winter).
  • Fuel Valve/Petcock: This little valve controls the flow of fuel from the tank to the carburetor. Ensure it's turned "ON" and that the valve isn't clogged. Remove the fuel line from the carburetor and turn the petcock on. Fuel should flow freely. If not, the petcock may need cleaning or replacement.
  • Fuel Line: Check the fuel line for kinks, cracks, or blockages. Replace it if necessary.

  • Carburetor: The carburetor mixes fuel and air. This is a frequent source of starting problems.

    • Clogged Jets: The carburetor's jets are tiny orifices that meter fuel flow. These are easily clogged by debris. The pilot jet, in particular, is notorious for causing starting issues. Remove the carburetor, disassemble it carefully (taking pictures as you go!), and clean the jets with carburetor cleaner and a small wire or jet cleaning tool. Never use a drill bit as this can damage the jet.
    • Float and Needle Valve: The float controls the fuel level in the carburetor bowl. If the float is stuck or the needle valve is not sealing properly, the carburetor may flood (too much fuel) or starve (not enough fuel). Inspect the float for damage and ensure it moves freely. Clean the needle valve and its seat.
    • Pilot Screw Adjustment: The pilot screw controls the air/fuel mixture at idle and low speeds. A misadjusted pilot screw can make starting difficult. Refer to your PW50's service manual for the correct setting. As a starting point, try turning the screw all the way in (gently!) and then backing it out 1.5 turns.
  • Air Filter: A dirty or clogged air filter can restrict airflow and cause a rich fuel mixture, making starting difficult. Clean or replace the air filter regularly.

Sparky, Sparky, Boom, Boom! Is There a Healthy Spark?

If fuel delivery seems okay, let's check the ignition system. A healthy spark is essential for igniting the air/fuel mixture.

  • Spark Plug: Remove the spark plug and inspect it.

    • Wet Spark Plug: Indicates flooding. Dry the spark plug and try again.
    • Fouled Spark Plug (black and oily): Indicates a rich fuel mixture or excessive oil. Replace the spark plug.
    • Clean and Dry Spark Plug: Indicates a lean fuel mixture or no fuel delivery.
    • Check for Spark: Reconnect the spark plug to the spark plug wire. Hold the plug against the engine cylinder head (to ground it) and crank the engine. You should see a bright blue spark jumping across the spark plug gap. If the spark is weak, yellow, or non-existent, proceed to the next steps. Be careful not to touch the spark plug while cranking the engine, as you could get a shock.
  • Spark Plug Wire and Cap: Inspect the spark plug wire and cap for damage or corrosion. Ensure the cap is securely attached to the spark plug.
  • Ignition Coil: The ignition coil amplifies the voltage to create a strong spark. If the coil is faulty, it won't produce enough voltage. Testing the ignition coil requires a multimeter and a service manual. If you suspect the coil is bad, it's best to replace it.
  • Stator/Magneto: The stator generates the electrical power for the ignition system. A faulty stator can cause a weak or no spark. Testing the stator requires a multimeter and a service manual.
  • Kill Switch: The kill switch is designed to stop the engine. Make sure the kill switch is in the "RUN" position. A faulty kill switch can prevent the engine from starting. Disconnect the kill switch to rule it out as a problem.

Compression: The Heart of the Engine

Compression is crucial for proper combustion. Low compression means the engine can't effectively compress the air/fuel mixture, making it difficult or impossible to start.

  • Compression Test: The best way to check compression is with a compression tester. Remove the spark plug and screw the compression tester into the spark plug hole. Crank the engine several times and note the reading on the tester. Refer to your PW50's service manual for the correct compression specification.

  • Possible Causes of Low Compression:

    • Worn Piston Rings: Piston rings seal the gap between the piston and the cylinder wall. Worn rings allow compression to leak past the piston.
    • Worn Cylinder: A worn cylinder can also cause low compression.
    • Leaking Head Gasket: The head gasket seals the cylinder head to the cylinder. A leaking head gasket can cause compression to leak out.
    • Damaged Valves (less common on PW50): While less likely on a PW50 due to its simple design, damaged valves can also cause low compression.

Air Intake: Let the Engine Breathe

A blocked air intake can choke the engine and prevent it from starting.

  • Air Filter: As mentioned earlier, a dirty or clogged air filter restricts airflow. Clean or replace the air filter.
  • Air Intake Boot: Check the air intake boot (the rubber hose that connects the air filter to the carburetor) for cracks or leaks.
  • Obstructions: Make sure there are no obstructions in the air intake path.

Electrical Gremlins: Chasing the Ghosts

While less common than fuel or spark issues on a PW50, electrical problems can still cause starting difficulties.

  • Wiring Harness: Inspect the wiring harness for damaged or corroded wires.
  • Ground Connections: Ensure all ground connections are clean and secure.
  • CDI Unit (Capacitor Discharge Ignition): The CDI unit controls the timing of the spark. A faulty CDI unit can prevent the engine from starting. Testing the CDI unit requires specialized equipment.

Specific PW50 Quirks to Watch Out For

The PW50 has a few unique characteristics that can contribute to starting problems:

  • Oil Injection System: The PW50 uses an oil injection system to lubricate the engine. If the oil injection system is not working properly, the engine may not start or may seize. Ensure the oil tank is full and the oil pump is functioning correctly. You can usually see the oil pump lever moving when the throttle is twisted.
  • Automatic Choke (Some Models): Some PW50 models have an automatic choke. A malfunctioning automatic choke can cause starting problems.
  • Training Wheels: While not directly related to starting, training wheels can sometimes interfere with the rider's ability to kickstart the bike properly. Make sure the bike is stable and the rider can get a full, strong kick.

Kickstarting Technique: It Matters!

Even with everything else in order, poor kickstarting technique can prevent the PW50 from starting. Here's a proper technique:

  1. Turn on the fuel.
  2. Pull the choke (if equipped).
  3. Slowly push the kickstarter down until you feel resistance (this is the compression stroke).
  4. Release the kickstarter and give it a full, strong kick.
  5. Repeat as needed.

Avoid "choppy" or weak kicks. A smooth, full kick is essential.

Frequently Asked Questions

  • Why is my PW50 flooding? Flooding is often caused by a stuck float or a leaking needle valve in the carburetor, allowing too much fuel into the engine. Clean or replace these components.
  • How do I clean the carburetor jets? Carefully disassemble the carburetor, remove the jets, and clean them with carburetor cleaner and a small wire or jet cleaning tool.
  • What kind of spark plug does my PW50 need? Refer to your PW50's service manual for the correct spark plug type. Using the wrong spark plug can cause starting problems.
  • My PW50 starts but dies immediately. What's wrong? This is often caused by a clogged pilot jet in the carburetor or a misadjusted pilot screw. Clean the carburetor and adjust the pilot screw.
  • How often should I clean the air filter? Clean the air filter regularly, depending on riding conditions. In dusty conditions, clean it after every ride.

Conclusion

Troubleshooting a non-starting PW50 can seem daunting, but by systematically checking the fuel delivery, spark, compression, and air intake, you can usually pinpoint the problem. Remember to start with the simplest solutions first and work your way up to the more complex ones. With a little patience and persistence, you'll have your little rider back on the PW50 in no time. Always consult your PW50's service manual for specific instructions and specifications.