The duration for which you can leave the choke engaged while starting a motorcycle engine without causing damage can vary depending on various factors, including the specific motorcycle model and its carburetor tuning. However, as a general guideline, it is recommended to use the choke only during the initial start-up phase and gradually disengage it as the engine warms up.
Typically, once the engine has started, you should begin to adjust the choke by gradually reducing its engagement or turning it off completely as the engine starts to run smoothly. This process usually takes a few minutes, but it can vary depending on the ambient temperature and other factors.
Leaving the choke engaged for an extended period can result in an overly rich fuel mixture, which can lead to fouled spark plugs, reduced fuel efficiency, and carbon buildup in the engine. It is generally not recommended to keep the choke engaged for more than a few minutes after the engine has started running.
In such cases, the choke is usually replaced by an enrichening system controlled by the engine control unit (ECU). These systems automatically adjust the air-fuel mixture during startup and warm-up, eliminating the need for manual choke operation.
To get accurate and specific instructions for your particular motorcycle model, it's always best to refer to the owner's manual provided by the manufacturer. The manual should provide detailed information on how to properly operate the choke or enrichening system for your motorcycle's engine.