Why does the engine speed increase but the car speed doesn't when stepping on the accelerator?

[Harley]

When the engine speed increases but the car speed doesn't when stepping on the accelerator, it may be caused by slipping due to worn clutch plates. Here are specific details about engine speed: 1. 800/min~1200/min: During cold starts, if the idle speed is below 800/min or above 1200/min, it indicates poor engine condition. 2. Below 2000r/min: Try to avoid letting the engine operate below 2000r/min while driving. If the speed is too low, the engine will lack power, and the excessive load at low speeds can damage the engine and easily lead to carbon buildup. 3. Above 4000r/min: When the engine operates above 4000r/min, the combustion time shortens, leading to incomplete fuel combustion and a significant increase in fuel consumption. If driving normally in fifth gear, the speed usually reaches 150km/h, which is already a relatively dangerous speed. 4. 2200~3500r/min: The engine operates most economically and performs best within the 2200~3500r/min range. It is advisable to maintain the engine speed within this range during regular use.