Why my dirt bike won't start

[Smokingsmarties420]

I own a yz125 year 2000 it didn't have much pressure after the rebuild and after I was done it started up on 3rd kick ran fine for a second then shut down now it has so much pressure it's hard to kick like a 4 stroke almost and it won't start all it does is shoot flames can someone help me? I've taken exhaust off thinking they might be clogged but they aren't

 

[Clark Jeff]

A dirt bike that won't start can be caused by various factors, and diagnosing the issue requires a systematic approach. Here are some common reasons why a dirt bike may not start and steps to troubleshoot each issue:

1. Fuel Issues:
   • Empty Fuel Tank: Ensure there is enough fuel in the tank.
   • Fuel Quality: Old or contaminated fuel can lead to starting problems. Drain and replace with fresh gasoline.
   • Fuel Valve: Make sure the fuel valve (if equipped) is in the correct position.
2. Ignition System:
   • Spark Plug: Check the spark plug for fouling, damage, or wear. Replace it if necessary.
   • Ignition Coil: Inspect the ignition coil, spark plug wire, and connections for damage or loose connections.
   • Kill Switch: Ensure the kill switch is in the "run" or "on" position.
   • Ignition Timing: Verify that the ignition timing is correct.
3. Air and Ventilation:
   • Air Filter: A clogged or dirty air filter can restrict airflow. Clean or replace the air filter if necessary.
   • Ventilation: Ensure the gas tank and fuel cap vent properly to allow air into the tank as fuel is consumed.
4. Compression:
   • Low engine compression can prevent starting. Perform a compression test to check for adequate compression levels.
5. Electrical System:
   • Check the battery's charge and connections. Weak or dead batteries can cause starting issues.
   • Inspect the starter motor and solenoid for proper operation.
   • Ensure all electrical connections, wires, and switches are in good condition.
6. Carburetor and Fuel System:
   • A clogged or dirty carburetor can hinder starting. Clean or rebuild the carburetor if necessary.
   • Check the fuel filter and fuel lines for blockages or damage.
   • Verify that the choke is functioning correctly.
7. Safety Switches:
   • Many dirt bikes have safety switches (e.g., clutch lever or side stand switch) that need to be engaged for the engine to start. Make sure these switches are functioning correctly.
8. Exhaust and Muffler:
   • A severely blocked or damaged exhaust system can affect engine performance. Inspect the exhaust for obstructions.
9. Stale Fuel: If the dirt bike has been sitting for an extended period with old fuel, the fuel may have degraded. Drain the old fuel and refill with fresh gasoline.
10. Valve Clearance: Incorrect valve clearance can lead to starting problems. Check and adjust the valve clearances if necessary.
11. Starter Mechanism: If the electric starter or kickstarter mechanism is faulty or damaged, it can prevent the engine from turning over.
12. Mechanical Issues: More serious issues such as a seized engine, damaged piston, or worn-out components can also prevent starting.

If you have checked these common issues and your dirt bike still won't start, it's advisable to seek help from a qualified motorcycle mechanic or a dealership. They can perform a more comprehensive diagnosis and address any underlying problems.