4 Stroke Dirt Bike Won’t Start? (Common Issues & How to Fix)

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I have some good news and bad news when it comes to getting your dirt bike started. The good is that we should be able to get your bike started. The bad? We may have to try a few things first. Below, we’ll look at the steps (in order) of what we need to check if your 4 stroke dirt bike won’t start.

How to Start a 4 Stroke Dirt Bike

These are the top ten reasons a 4 stroke won’t start. It’s important to start with the simple items first, and work through the more difficult (costly) items. If you can start here, chances are you’ll get your dirt bike running again with a little patience.

  1. Gas is turned OFF
  2. No gas / old/bad gas (use this gas)
  3. Choke not working
  4. Carburetor or fuel injector is clogged/dirty
  5. Air filter is dirty (how to clean air filter)
  6. Jet in carb is faulty
  7. Battery needs replaced / charged
  8. No spark from plug / fouled spark plug
  9. Faulty kill switch
  10. Low compression

If your 4 stroke has fuel and spark but won’t start, you’ll want to exhaust the list above before taking your bike into a mechanic.

Check Spark Plug Condition

Spark Plug Comparison

How to Inspect a Spark Plug

Many dirt bikes use spark plugs that have an iridium tip in the center electrode, and they have a platinum tip in side electrode. Because of the iridium tipped plugs, make sure to read through the following before looking at the spark plug.

  • Do not try to clean the spark plug.
    If the spark plug or an electrode is dirty or has any objects (including dirt) replace the plug.
  • Use only a “wire-type feeler gauge” to check the spark.
    Never use a leaf-type feeler gauge when inspecting the spark plug.

Steps to Inspect a Spark Plug

If you’re testing a new plug, ride around for 10-15 minutes before taking a plug reading. A new spark plug will take some time for the initial coloring to take place.

Also, in order to get an accurate reading, get your RPMs up and going on a straightaway… Push the “kill switch” and pull in the clutch. Coast to a stop, then remove and inspect the spark plug.

  1. Remove the fuel tank
  2. Disconnect the spark plug cap
  3. Remove the spark plug
  4. Inspect the electrode, the gasket, and the insulator
    The “white” insulator around the electrode should be tan or medium-gray.White (or light gray) = too lean
    Black (or fouled) = too richIf there is any dirt or debris, simply replace the spark plug.
  5. Check the plug gap
    If the gap is out of spec, replace with new.
  6. Reinstall spark plug (or install new)
    Tighten by hand until snug and then with a wrench until gasket is compressed ( 1/2 turn for new) or (1/8 – 1/4 turn for used).
  7. Connect the spark plug cap
  8. Reinstall fuel tank

Does the spark plug look bad? Possible causes include:

• Incorrect spark plug heat range
• Spark plug gap is incorrect
• Dirty air cleaner element

Try the “Spark Test”

Spark Plug

How to Test a 4 Stroke Spark Plug for Spark?

Testing to see whether a plug has spark is actually pretty easy. Here’s how you do it:

  • Remove spark plug
  • Connect to plug wire/boot
  • Hold the rubber boot (so you don’t get shocked) so that the plug is against head of engine
  • Turn the bike over

You are watching for spark to come from the spark plug gap.

Weak or No Spark? Here are the possible issues:

• Bad spark plug
• Ignition control module is faulty
• Alternator is faulty
• Bad coil
• Broken or shorted spark plug wire
• Faulty ignition pulse generator
• Kill switch is bad

How to Start a 4 Stroke Dirt Bike

Starting a Cold 4 Stroke

  • Turn the fuel valve ON.
  • Shift the transmission into neutral.
  • If the temperature is 35°C (95°F) or below, pull the choke knob fully out.
  • If the temperature is below 0°C (32°F), open the throttle two or three times. (The engine requires a richer mixture for starting in cold weather. When the throttle is so opened, the accelerator pump will feed extra fuel to the cylinder, thereby facilitating starting in cold weather.)
  • With the throttle closed, operate the kickstarter start- ing from the top of the kickstarter stroke, kick through to the bottom with a rapid, continuous motion. (Do not open the throttle, As the carburetor is equipped with an accelerator pump, excessive fuel will be charged into the engine, and the spark plug will be fouled if the throttle is opened and closed repeatedly. Excessive fuel in the engine makes kick- starting difficult.)
  • About a minute after the engine starts, push the choke knob back all the way to fully OFF. If idling is unstable, open the throttle slightly.

Starting a Hot 4 Stroke

  • Turn the fuel valve ON
  • Shift the transmission into neutral
  • Pull the hot start lever and kick-start the engine. (Do not open the throttle)
  • As soon as the engine starts, release the hot start lever

Starting a 4 Stroke While Out Riding

  • Shift the transmission into neutral
  • Pull the hot start lever and kick-start the engine. (Do not open the throttle)
  • As soon as the engine starts, release the hot start lever

Starting a Flooded 4 Stroke Dirt Bike

If you’ve been trying to start your bike for a while (and using the gas, even though you normally shouldn’t) and you aren’t able to get the bike started, it could just be flooded.

So, if you’re flooded dirt bike won’t start, try this:

  1. Let the bike rest for 5-10 minutes
  2. Make sure the choke is off
  3. Make sure the ignition is on
  4. Hold the throttle wide open
  5. Kick (or push start) the engine to get it turning over
  6. As soon as the engine starts, release the throttle