How do you balance a motorbike carburettor?

Before the oil in a motorbike enters the cylinder for combustion, it must first undergo an atomisation process to mix the oil and air into oil and gas for combustion. This atomised concentration of oil and air is known as the mixing ratio.

What are the effects of different mixing ratios on the car? If the mixture is too lean, the engine will tend to overheat, leading to stalling and even shrinkage. If the mixture is too rich, the engine will consume more fuel and will easily stall after warming up, which will cause the engine to build up carbon over time. Therefore, neither too thin nor too thick is a good thing, especially when it is too thin, it will have a direct negative impact.

There are many factors that affect the mixture ratio on a carburettor, but the one that is generally best known is the mixture ratio screw on the carburettor. This is the simplest way of adjusting the mixture ratio, and when you talk about adjusting the mixture ratio, you are mostly referring to the mixture ratio screw. So in this article we will only talk about the principle of the mix ratio screw and how it is adjusted, other factors involved in the mix ratio will not be discussed for the time being to avoid beginners not knowing where to start.

The mix ratio screw is located on the carburettor and can be found on the carburettor housing. It is usually a small flat head screw (the larger ones that can be turned by hand are usually the idle speed screws), although there may be exceptions, depending on the type of car or carburettor.

How does the mix ratio screw work to control the mix ratio? This is the basic structure of a carburettor. Air flows rapidly through this area and is sucked up through the nozzle to atomise the oil. According to this basic structure, it is not easy to adjust the ratio of air and oil intake, so the general practice is to design a small air path on the outside, so that air can be introduced through this air path at the same time, and then make a small valve on this air path to control the amount of air intake to this bypass air path, to achieve the purpose of adjusting the mixing ratio. The mix ratio screw is located in this air path and acts as a valve. 

By adjusting the mix ratio screw in and out, the valve can be opened and closed to different degrees to regulate the amount of air introduced into the bypass.

Therefore, in this configuration, when the mix ratio screw is turned "in", the bypass air passage becomes narrower, the air intake becomes less, and the oil and gas becomes thicker (A/F decreases); when the mix ratio screw is turned "out", the bypass air passage becomes wider, the air intake becomes more, and the oil and gas becomes thinner (A/F increases).