What is the reason why the motorcycle can't come down without turning off the throttle?

Of course, if the motorcycle does not turn off the throttle, the engine speed will not drop. If the engine speed drops by itself without closing the throttle, it is a fault.

If the motorcycle has turned off the throttle, but the engine speed is still delayed, it is generally caused by the throttle pipe and throttle sleeve being stuck, or the carburetor being improperly debugged, and the carburetor throttle or throttle plunger and oil needle being stuck and unable to return.

In this case, it is necessary to check whether the throttle handle sleeve and throttle wire are damaged, or the installation and debugging wiring is incorrect, which leads to the jam and the throttle cannot return. Check and clean the carburetor, check whether the mixing ratio, oil level and oil needle of the carburetor are improperly adjusted, whether the throttle plunger is stuck for various reasons, and whether the air door is faulty.

In other aspects, you can also check whether there is slight air leakage in the engine valve, intake pipe and other hoses. Although air leakage will generally cause failures such as easy flameout without idling, or difficulty in starting and failure to start, it may also cause the engine speed not to drop after adding. In addition, check whether there is any problem with the quality of gasoline and whether the engine is overheated at high temperature, which may sometimes cause this failure.