* Float Level: The most probable cause. The float in the carburetor controls the fuel level. If the float is stuck, damaged, or the float needle valve is worn or dirty, fuel will continue to flow into the carburetor even when the engine is off. When the engine cools, the fuel expands less, leading to overflow. A rich fuel mixture (too much fuel) when you try to start it will prevent ignition.
* Float Needle Valve: This valve, located inside the carburetor, seals the float bowl. If it's not sealing properly (due to wear, debris, or a bent needle), fuel will leak past it.
* Carburetor Diaphragms: These rubber diaphragms control fuel flow. If cracked or deteriorated, they can leak and cause overflow, especially when the engine cools and vacuum changes.
* Fuel Pump (less likely, but possible): While less likely to be the direct cause of leaking *from* the carburetor when cold, a faulty fuel pump could create excess pressure in the system, contributing to the overflow. A failing pump might also struggle to prime after the system has cooled, resulting in starting issues.
Why you have to shut the fuel line: This confirms that the problem is an excess of fuel in the carburetor. The engine floods because there's too much gasoline in the combustion chamber.
What to do:
1. Safety First: Disconnect the battery negative terminal before working on the fuel system. Gasoline is highly flammable.
2. Visual Inspection: Carefully examine the carburetors. Look for any visible fuel leaks around the float bowls.
3. Float Level Check: This requires carburetor removal and disassembly. Consult a CX500 service manual for instructions specific to your motorcycle. The manual will show you how to check and adjust the float level to ensure it's within specifications.
4. Float Needle Valve Check: As part of the carburetor disassembly, inspect the float needle valve for wear, damage, or debris. Clean or replace it as necessary.
5. Diaphragm Inspection: Carefully examine the carburetor diaphragms for cracks, tears, or deterioration. Replace any damaged diaphragms.
6. Carburetor Cleaning: Even if you don't find major issues, thoroughly clean the carburetors using carburetor cleaner and compressed air. This removes any accumulated debris that might be interfering with proper operation.
If you're not comfortable working on carburetors: Take your motorcycle to a qualified motorcycle mechanic. Carburetor repair requires specialized tools and knowledge. Attempting it without experience can lead to further damage. A properly functioning CX500 carburetor is crucial for its performance and reliability.
