There can be several reasons why a motorcycle's engine might require higher revs before starting:
Cold engine: When the engine is cold, the fuel mixture may not vaporize easily, resulting in a lean mixture. A lean fuel mixture can make it more challenging for the engine to ignite and start. Revving the engine can help increase the fuel flow and temperature, aiding in the combustion process.
Weak battery: If the motorcycle's battery is weak or low on charge, it may not provide enough electrical power to crank the engine effectively. Revving the engine before starting can help generate additional electricity and increase the charging rate of the battery, potentially providing enough power to start the motorcycle.
Carburetor or fuel injection system issues: If the motorcycle has a carburetor, it relies on a precise fuel-air mixture for smooth starting. If the carburetor is dirty, clogged, or out of adjustment, it may not deliver the correct fuel-air ratio, making it necessary to rev the engine to compensate for the inadequate mixture. Similarly, motorcycles equipped with a fuel injection system may require higher revs if there are issues with the fuel injectors or sensors, affecting the fuel delivery.
Choke or enrichener usage: Motorcycles equipped with a choke or enrichener (a device that restricts airflow to create a richer fuel mixture) may require higher revs before starting, especially when the engine is cold. Engaging the choke or enrichener enriches the fuel mixture, making it easier for the engine to start and run smoothly.
Engine tuning: If the motorcycle's engine is not properly tuned, it may require higher revs before starting. Incorrectly adjusted valves, ignition timing, or fuel-air mixture can affect the engine's starting characteristics.
It's important to note that while occasional higher revs before starting may be necessary in certain situations, excessively high revving can cause engine wear and potential damage. If you consistently experience difficulties starting your motorcycle, it's advisable to have it inspected by a qualified mechanic to identify and address any underlying issues.