Analysis of the reasons for the abnormal oil level of the carburetor
As a key part of the engine, the carburetor shoulders the primary mission of mixing a certain proportion of gasoline and air , thus requiring our extra care. Especially with the warming of the weather, the number of motorcycle trips has also increased. At this time, various problems on the carburetor will appear immediately, and its normal protection has also become an indispensable content.
The oil level in the float chamber of the motorcycle carburetor not only affects the power and economy of the vehicle, but also seriously affects the life and emission quality of the engine. At present, in the social ownership of motorcycles in my country, more than 99% of the motorcycles adopt carburetors. According to statistics, about 10% to 15% of motorcycles have abnormal oil levels, which not only provides motorcycle users with a problem. It has brought economic losses and caused serious pollution to the environment.
I. The principle of controlling the oil level of the carburetor
With the operation of the engine, the heavy oil level of the carburetor falls, and the float drives the needle valve to fall When the oil level in the float chamber reaches the set value, the float drives the needle valve to rise, and the needle valve and the needle valve seat form a sealing working surface (closed annulus), it is forbidden for fuel to continuously enter the float chamber. During the operation of the engine, the oil level in the float chamber is kept within the set value range through the continuous separation and combination of the needle valve and the needle valve seat, so as to ensure that the engine works in the best state.
2. Reasons for abnormal oil level
1. Oil level is too low
If the oil level of the oiler is too low, it is because the adjustment is improper. In order to seek low fuel consumption of the vehicle, some riders and maintenance personnel blindly raise the float to lower the oil level in the float chamber, and use the engine to absorb less fuel at the same speed to reduce fuel consumption. The above method is worthless.
2. The oil level is too high
a) The working surface of the needle valve and needle valve seat seal oil is worn out
A large number of practice shows that the wear of the needle valve is the most serious. The normal needle valve forms a sealing working surface through its own progressive slope and the active centering of the bottom end ring of the valve seat. If the automatic centering seal cannot be performed, the fuel will continue to flow into the float chamber, causing the oil level to be too high.
b) The replacement parts are not suitable
The clearance between the needle valve and the guide sleeve is 0.10~0.15mm, if the clearance is too small, it will affect the oil inlet The opening and closing of the carburetor will cause the oil level of the carburetor to be out of control, but this kind of failure phenomenon is rare; if the gap between the two is too large, the needle valve will not coincide with the center line of the guide sleeve during the rising process, resulting in the needle valve in the guide sleeve. In the middle of the stuck, the needle valve and the needle valve seat cannot be actively centered to form a sealing working surface, resulting in the oil level being too high. When designing a needle valve, it is necessary to reflect on the length and maximum diameter of the original needle valve.
c) Caused by impurities in the fuel
If the filter device in the fuel passage is damaged, it will cause the fuel to flow into the carburetor float chamber during the process Impurities are stuck between the needle valve and the needle valve seat, and the two cannot form a sealing working surface. When the oil level in the float chamber reaches the set value, the fuel will continue to flow into the float chamber.
d) Float leaks oil
If the float is not well sealed, the gasoline in the float chamber will seep into the float, causing the mass of the float to increase and the oil level to reach the set point. When the value is fixed, the float cannot float normally, and the needle valve cannot close the fuel passage, which causes the oil level to be too high.
e)Other reasons
The oil level may be out of control due to the sticking of the float shaft and excessive bumps due to poor road conditions.
Three, the persecution of abnormal oil level
1. The oil level is too low
oil If the surface is too low, the gasoline composition in the mixed gas will become thinner. In addition to difficult starting, fueling and stalling, and insufficient power, there are more serious problems:
1) During the process of the mixed gas entering the cylinder, gasoline Further atomization of the cylinder will absorb some of the heat and reduce the temperature of the piston, cylinder block and cylinder head. If the mixed gas is too thin, the working temperature of the engine will increase, the performance of the oil will be reduced, and the wear of the parts will be accelerated.
2) If the mixed gas is too lean, the distance between gasoline molecules in the mixed gas becomes larger, and the combustion speed becomes slower. Most of the heat generated by combustion is absorbed by the piston, cylinder block and cylinder head, causing the engine temperature to rise further. , and sometimes the combustion continues until the intake stroke of the next working cycle, causing the carburetor to backfire, the engine burns irregularly, the power is reduced, and the fuel consumption is increased.
2. The oil level is too high
If the oil level is too high, on the one hand, the fuel will be directly leaked from the carburetor oil spill pipe, resulting in direct loss of fuel ; On the other hand, it will cause the mixed gas to be too thick, resulting in:
1) The gasoline in the mixed gas is poorly atomized, and the bulk gasoline particles will wash the oil film on the cylinder wall and the surface of the piston, speeding up the operation of the parts. wear.
2) The gasoline cannot be completely burned, and part of the gasoline is discharged from the exhaust port, and the repeated combustion of the hot gas in the exhaust muffler causes the exhaust pipe to shoot, and the fuel consumption increases greatly. Statistics show that the fuel consumption when the oil level is too high is 200%~300% higher than that in normal combustion.
3) Incomplete combustion will produce a large amount of carbon deposits, which will accelerate the wear of piston rings; reduce the volume of the combustion chamber, the shrinkage ratio will become larger, the engine will burn irregularly, and the power performance will be reduced; a large amount of carbon deposits will be deposited in the combustion chamber. It may become a hot spot, causing the engine to fail to turn off, causing great damage to the engine.
4) The carbon monoxide and hydrocarbons emitted by the combustion of excessively rich mixed gas are 2~3 times that of normal combustion, which are the primary factors causing urban pollution.
