* Oil in the ignition coil: This is the most likely scenario. Oil is an excellent insulator, and if it contaminates the high-voltage components of the ignition system (coil, wires, spark plug cap), it will severely hinder or completely prevent spark generation. The oil might be leaking from a gasket or seal near the coil, or the coil itself might be cracked or damaged allowing oil intrusion.
* Oil in the spark plug boot/cap: Similar to the coil, oil in the spark plug cap will prevent a good connection and result in a weak or absent spark. Check for any visible oil residue around the cap.
* Crankcase breather system issues: A faulty crankcase breather system can allow excessive crankcase pressure to build, forcing oil into areas it shouldn't go, including the ignition system. This is less likely to directly cause spark issues, but could contribute to oil reaching the ignition components via other leaks.
* Loose or damaged spark plug wire(s): While not directly related to oil, loose or damaged wires can exacerbate the problem. If there's already a weak spark due to oil contamination, a faulty connection will make it worse.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect the entire ignition system, paying close attention to the coil, spark plug cap, and wires. Look for any signs of oil leakage or contamination. Wipe down any oily areas thoroughly with a clean rag and degreaser.
2. Spark Plug Check: Remove the spark plug, inspect it for oil contamination, and test it for spark using a spark tester (highly recommended) or by grounding it to the engine and cranking the engine. A healthy spark should be a bright blue and jump a noticeable gap.
3. Coil Check: If possible, test the coil's resistance with a multimeter. This requires knowing the correct resistance specifications for your specific XL250 model. (Consult a service manual). A faulty coil is often a culprit in ignition problems.
4. Check the Crankcase Breather System: Inspect the breather hoses and related components for blockages or damage. Ensure they are correctly routed and connected.
5. Oil Level: Make sure you aren't overfilling the engine with oil. Excessive oil pressure can exacerbate existing leaks.
6. Check for other leaks: Look for oil leaks in other areas of the engine. A significant oil leak could be indicative of a more serious problem requiring professional attention.
Important Note: If you're not comfortable working on motorcycles, take it to a qualified mechanic. Improperly handling the ignition system can be dangerous due to the high voltage involved. A service manual for your specific Honda XL250 year and model is invaluable during this troubleshooting process.
