If a KTM Duke 250 is kept idle without being used, there are a few factors to consider in determining how long it can be kept in idle condition:
Fuel: Fuel can degrade over time, especially if it contains ethanol. Ethanol-blended fuel can absorb moisture from the air, leading to phase separation and potential damage to the fuel system. It is recommended to use fuel stabilizers or drain the fuel tank before long periods of inactivity. The specific recommendations from KTM can be found in the owner's manual.
Battery: The battery can gradually discharge when the bike is idle, especially if it is not connected to a battery maintainer or charger. The time it takes for the battery to discharge completely can vary based on various factors such as the condition of the battery, ambient temperature, and any electrical draws from the bike's systems. It is generally advisable to periodically charge the battery or use a battery maintainer to prevent it from discharging completely.
Lubrication: When a motorcycle is not used for an extended period, the oil in the engine may settle and certain parts may not be adequately lubricated. It is recommended to periodically start the bike and let it idle for a short duration to circulate the oil and ensure proper lubrication.
Overall, it is generally not recommended to keep a motorcycle idle for an extended period without any maintenance or usage. If you anticipate leaving the Duke 250 unused for a significant amount of time, it would be beneficial to follow the manufacturer's guidelines for storage or consult with a KTM dealership for specific recommendations to ensure the bike remains in good condition.