How to adjust the fuel surface of motorcycle carburetor when it is low?

Carburetor fuel surface is by adjusting a small iron of the top float needle above the float to adjust. Make it up and down to pull the iron so that it can adjust the fuel surface height. However, there is also a kind of all plastic float. The top float needle is plastic piece can't adjust. Therefore, if the fuel surface is not normal, it may change in carburetor, change float or float needle.

In fact, there is a grease drain screw at the bottom of the carburetor, with a root tube. Connect a transparent pipe to the top, screw loose the fuel screw, one end of the transparent pipe to the fuel outlet, and the other end is up. According to the principle of U-shaped pipe, the height of the fuel surface in the pipe is the height of the fuel surface in the carburetor.

 
Generally speaking, the standard is on the joint line, but actually considering that there is some fuel in the pipe, so the actual level is about 1-2mm lower.

In fact, if the carburetor does not need to adjust, just keep it the original state. If the fuel surface is too high, the engine mixture is too thick, the acceleration is weak, the combustion chamber and exhaust carbon is serious, or the motorcycle fuel consumption is high, then it will need to adjust the carburetor. 

If the carburetor fuel surface is too low, the engine is overheated, the motorcycle is slow or the motorcycle is unable to climb, then it will need to adjust the carburetor. If not, it is not recommended to adjust, especially the carburetor of high-grade motorcycles, rarely need to adjust. In this situation, to adjust the fuel needle is feasible. However, my approach is to find a very thin metal gasket directly set on the fuel needle back to the original place, since the direct adjustment of the fuel supply will be too large, resulting in high fuel consumption.