The Yamaha PW80 – a beloved mini-moto for generations of budding riders. It's simple, reliable, and a fantastic introduction to the world of motorcycling. However, even the most dependable machines can throw a wrench (or spark plug) into the works sometimes, and starting problems are a common frustration for PW80 owners. Let's dive into the most frequent culprits and how to troubleshoot them, so you can get your little ripper back on the track (or backyard) in no time.

Okay, My PW80 Won't Start. Where Do I Even Begin?

Before you start tearing the engine apart, let's cover the basics. Think of this as your PW80 starting problem triage.

  • Is there fuel? Sounds obvious, but check the fuel tank. Stale fuel can also be a problem, especially if the bike has been sitting for a while. Drain the old fuel and replace it with fresh stuff.
  • Is the fuel valve open? Make sure the petcock (fuel valve) is in the "ON" position. Sometimes, it's easy to overlook.
  • Is the choke engaged? If the engine is cold, the choke enriches the fuel mixture for easier starting. Try starting with the choke on, and if it doesn't start, try with it off.
  • Is the kill switch engaged? This is another easy-to-miss culprit. Make sure the kill switch is in the "RUN" position.
  • Is the spark plug wire securely connected? A loose connection can prevent the spark plug from firing.

If you've checked all these basics and the PW80 still refuses to start, it's time to dig a little deeper.

Spark, Fuel, and Compression: The Holy Trinity of Internal Combustion

An engine needs three things to run: spark, fuel, and compression. If any of these are missing or insufficient, you'll have starting problems. Let's investigate each one.

No Spark? Let's Get Electrified!

A weak or non-existent spark is a common reason for a PW80 to refuse to start. Here's how to check and troubleshoot the ignition system:

  1. Check the Spark Plug:

    • Remove the spark plug: Carefully disconnect the spark plug wire and use a spark plug wrench to remove the plug from the cylinder head.
    • Inspect the spark plug: Look for signs of fouling (carbon buildup, oil, or fuel). A fouled plug won't spark properly. Clean the plug with a wire brush or replace it with a new one.
    • Check the spark gap: The gap between the electrode and the ground electrode should be within the manufacturer's specifications (usually around 0.024-0.028 inches). Use a spark plug gap tool to adjust the gap if necessary.
    • Test for spark: Reconnect the spark plug wire to the plug and hold the plug against the engine block (grounding it). Crank the engine over (either by kicking or using the electric start, if equipped). You should see a strong, blue spark jump across the gap. If the spark is weak, yellow, or non-existent, move on to the next steps.

  2. Inspect the Spark Plug Wire and Cap:

    • Check for damage: Look for cracks, cuts, or corrosion on the spark plug wire and cap. Replace them if they are damaged.
    • Ensure a secure connection: Make sure the spark plug wire is securely connected to the spark plug cap and to the ignition coil.

  3. Test the Ignition Coil:

    • Use a multimeter: A multimeter can be used to test the resistance of the ignition coil. Consult your PW80 service manual for the correct resistance values. If the resistance is outside the specified range, the coil may be faulty and need to be replaced.
    • Consider a replacement: Ignition coils can weaken over time. If you suspect the coil is the problem, replacing it is a relatively inexpensive and straightforward solution.

  4. Check the Stator and CDI Unit:

    • Stator: The stator generates the electricity that powers the ignition system. Testing the stator requires a multimeter and knowledge of electrical testing procedures. Consult your service manual for specific instructions.
    • CDI (Capacitor Discharge Ignition) Unit: The CDI unit controls the timing and intensity of the spark. CDI units are difficult to test without specialized equipment. If you've ruled out other ignition components, a faulty CDI unit could be the culprit. Replacing the CDI unit is often the best course of action in this case.

Important Note: When working with the ignition system, disconnect the battery (if equipped) to prevent electrical shock.

Fuel Delivery Problems: Is the PW80 Starving?

If you have spark, the next thing to check is the fuel system. A clogged carburetor or a fuel delivery problem can prevent the engine from starting.

  1. Clean the Carburetor:

    • Remove the carburetor: Disconnect the fuel line, throttle cable, and any other cables or hoses connected to the carburetor. Carefully remove the carburetor from the intake manifold.
    • Disassemble the carburetor: Take the carburetor apart, paying attention to the location of each component. It's helpful to take pictures as you disassemble it.
    • Clean the carburetor: Use carburetor cleaner to thoroughly clean all the jets, passages, and components. Pay close attention to the main jet, pilot jet, and needle jet. Use compressed air to blow out any remaining debris.
    • Reassemble the carburetor: Reassemble the carburetor, making sure all the components are properly installed.
    • Adjust the air/fuel mixture screw: Consult your service manual for the correct air/fuel mixture screw setting. This adjustment affects the engine's idle and low-speed performance.

  2. Check the Fuel Filter:

    • Locate the fuel filter: The fuel filter is usually located in the fuel line between the fuel tank and the carburetor.
    • Inspect the fuel filter: Check the fuel filter for clogs or debris. Replace the filter if it is dirty or clogged.

  3. Check the Fuel Lines:

    • Inspect the fuel lines: Look for cracks, kinks, or leaks in the fuel lines. Replace any damaged fuel lines.
    • Ensure proper routing: Make sure the fuel lines are routed correctly and are not pinched or restricted.

  4. Check the Fuel Tank Vent:

    • Ensure proper venting: The fuel tank needs to vent properly to allow fuel to flow freely. A clogged vent can create a vacuum in the tank, preventing fuel from reaching the carburetor. Check the vent for obstructions and clear it if necessary.

Compression Issues: Losing Power?

If you have spark and fuel, the next thing to check is compression. Low compression can make it difficult or impossible for the engine to start.

  1. Perform a Compression Test:

    • Use a compression tester: A compression tester is a gauge that measures the pressure inside the cylinder.
    • Remove the spark plug: Remove the spark plug from the cylinder head.
    • Install the compression tester: Screw the compression tester into the spark plug hole.
    • Crank the engine: Crank the engine over several times (usually 5-10 kicks) while holding the throttle wide open.
    • Read the compression reading: Note the highest reading on the compression tester.
    • Compare to specifications: Consult your service manual for the correct compression reading. If the reading is significantly lower than the specified value, there may be a compression problem.

  2. Possible Causes of Low Compression:

    • Worn piston rings: Worn piston rings are a common cause of low compression. The rings seal the gap between the piston and the cylinder wall, preventing combustion gases from escaping.
    • Worn cylinder: A worn cylinder can also cause low compression. Over time, the cylinder wall can become worn or damaged, reducing the effectiveness of the piston rings.
    • Leaking valves: Leaking valves can also cause low compression. The valves seal the combustion chamber, preventing gases from escaping.
    • Blown head gasket: A blown head gasket can cause low compression by allowing combustion gases to leak between the cylinder head and the cylinder.

Important Note: Addressing compression issues typically requires engine disassembly and repair. It's best to consult a qualified mechanic if you suspect a compression problem.

Other Potential Culprits

While spark, fuel, and compression are the primary suspects, here are a few other things to consider:

  • Timing Issues: Incorrect ignition timing can make it difficult to start the engine. This is less common on a PW80 but worth considering if you've exhausted other possibilities.
  • Air Leaks: Air leaks in the intake manifold or around the carburetor can disrupt the air/fuel mixture and make starting difficult.
  • Exhaust Obstruction: A blocked exhaust can prevent the engine from breathing properly.

Frequently Asked Questions (PW80 Starting Problems)

  • Why does my PW80 only start when it's cold? This often points to a carburetor issue, likely a clogged pilot jet. Clean the carburetor thoroughly.
  • My PW80 starts but then dies immediately. What's happening? This could be a fuel delivery problem, like a clogged fuel filter or a vacuum leak in the fuel lines.
  • How often should I change the spark plug on my PW80? It's recommended to replace the spark plug annually, or more frequently if you ride in dusty or dirty conditions.
  • What's the best way to clean a PW80 carburetor? Use a dedicated carburetor cleaner and compressed air to clear all jets and passages. Disassembly is necessary for a thorough cleaning.
  • My PW80 has been sitting for a long time. What should I do before trying to start it? Drain the old fuel, clean the carburetor, and check the spark plug. Fresh fuel is essential.

Getting Back on the Trail

Troubleshooting starting problems on a Yamaha PW80 can seem daunting at first, but by systematically checking the spark, fuel, and compression, you can usually pinpoint the problem. Remember to consult your service manual for specific instructions and specifications. With a little patience and persistence, you'll have your PW80 running smoothly again and your young rider back to enjoying the thrill of the ride. Don't be afraid to ask for help from experienced mechanics or online forums if you get stuck – the PW80 community is a helpful bunch.