For the proper operation of any engine based on the principle of internal combustion, optimal dosing of the air-fuel mixture (FA) is important. If the balance of the ratio is disturbed, the equipment begins to malfunction.
Even the most precise mechanisms require periodic adjustments. Adjusting the carburetor on a Chinese scooter is not a frequent procedure, but it is necessary for the proper functioning of the equipment.
Carburetor value
Today, there are several ways to supply fuel to the engine. They differ in their principle of operation, but all devices are united by a common parameter - preparing the exact amount of working mixture.
The carburetor is a simple but effective device for optimal dosing of fuel assemblies into the cylinders. The idea of its operation is simple - mix the required amount of fuel and air, and then feed the finished proportion into the engine.
The advantages of using a carburetor set it apart from other methods of preparing the mixture. The engine itself controls how much fuel it needs to receive.
Required Tools
Husqvarna special screwdriver
The main tool for adjusting the carburetor of a Chinese chainsaw is a medium-sized slotted screwdriver (flat type). Some saws require special keys, for example to set up the Husqvarna.
For more accurate and faster tuning, a tachometer is still required; it allows you to determine the engine speed, but this is not our case, our task is to learn how to tune by ear.
Read more about what tachometers are available, where to buy, how much they cost, and also how to set up a chainsaw with it.
For reference! This is the same as tuning a guitar. An experienced musician tunes by ear, while a beginner tunes using special instruments. In the case of a chainsaw, the opposite is true. An experienced person adjusts it with a tachometer, and a beginner tunes it by ear. In our repair shop, we use a high-quality and inexpensive tachometer from Aliexpress, which can be purchased at this link.
Buy tachometer on Aliexpress
Signs of necessary adjustment
The only parameter that the driver controls while driving is the throttle position. It affects the volume of mixture supplied to the scooter.
There are a number of signs by which you can determine the condition of the carburetor. These include:
- drop in engine power;
- failures when accelerating the scooter;
- hard start;
- increased fuel consumption;
- abnormal reaction to the accelerator handle;
- sudden engine stop.
Signs do not have a noticeable periodicity; they can occur at any time.
What is the carburetor of a Chinese scooter and its capabilities, disadvantages, tuning
The carburetor circuit of a Chinese scooter is, in principle, standard and suitable for both 2t and 4t engines. The design of the carburetor allows certain actions to be taken to improve its performance, however, if the engine is two-stroke, the efforts will not make sense.
The simplest approach is to replace the carburetor with a more advanced one, for example, with an accelerator motor, if you have a fairly old version without it. Most often, simple tuning is limited to replacing the main fuel jet, this is especially true for engines with low power. Replacing the nozzle helps to increase the fuel channel and, due to this, add a little power to the engine.
Maintenance Procedure
Scooter motors are manufactured in different volumes. The most common are 50 and 150 cubic meters. The gas distribution system has both 2t and 4t options. The differences between the models are minimal, so maintenance of 2 and 4 stroke 50cc mopeds is carried out according to the same principle.
The technique includes:
- Carburetor adjustment at idle speed. The scooter starts and its operation without load is analyzed. The assessment is carried out based on the evenness of the strokes and the stability of the engine speed.
- The position of the screws for the quantity and quality of the mixture is adjusted.
Due to the relative lightness of the structure, adjustment is made with two control bolts. If stable operation cannot be achieved, it is necessary to remove the unit and carry out deep cleaning and adjustment.
Important: before servicing the carburetor on a 4t and 2t scooter, you should make sure that the piston group and ignition system are in good condition. Otherwise, the adjustment will have no effect.
Removal
Because of the way it works, the carburetor is attached directly to the intake manifold. The fuel line and air duct are connected to it. All removable hoses are removed from the body and the part is exposed.
The starting enrichment is switched off. The fastening bolts are unscrewed with a spanner wrench, and the entire assembly is pulled out.
Installation is in the reverse order.
Carburetor cleaning
An excellent cleaning method is to blow out the internal channels with compressed air from a compressor. For this, a special gun with a pointed tip is used.
During operation, plaque forms on the surfaces of the carburetor. This is due to the quality of gasoline. Most of the dirt stops in the fuel filter, but some gets into the intake tract.
To remove deposits, you can use either a solvent or a special liquid for cleaning carburetors. It is also suitable for scooters. The advantage of using it is that the cleaning agent is under pressure and is able to penetrate into the most inaccessible channels.
The scooter carburetor has rubber gaskets. To avoid exposing them to cleaning mixtures, it is recommended to insulate these parts in advance.
When cleaning the intake mechanism of a scooter, it is not recommended to use fluffy rags. Their threads can get stuck in the carburetor components, which will lead to additional difficulties.
Idle speed adjustment
An indicator of proper operation of the carburetor on a scooter is a stable idle. The absence of “floating” speeds and confident operation indicate a prepared mixture inside the combustion chamber.
Regardless of 2 or 4 stroke engine options, you should start tuning by adjusting the idle speed. The number of cubes also does not matter.
For this purpose, there is a screw on the device that is responsible for dosing fuel when the scooter is operating without load.
Some carburetors do not have adjustment bolts. In this case, you need to adjust the idle mode using a needle and floats in the fuel chamber.
The scooter is started and allowed to run for a few minutes. This is necessary for better evaporation of gasoline inside the intake manifold and its mixing with air.
After warming up, turn the idle screw until the engine becomes stable. The criteria for correct adjustment are:
- the scooter maintains stable speed indicators;
- there is no engine tremors or failures in operation;
- the carburetor confidently switches to power gain mode (when over-throttled) and back.
Sometimes the scooter refuses to respond to idle adjustment. This behavior indicates additional problems in the intake system.
Mix quality
The two main components in the operation of any internal combustion engine are air and fuel. The force from their combustion pushes the pistons and forces the vehicle to move.
But simply mixing these substances is not enough. You can achieve maximum energy output only by maintaining the correct proportion of components. In a carburetor, this procedure is called adjusting the quality of the mixture and the entire operation of the 50cc scooter depends on it.
There are three types of air-fuel mass:
- poor;
- rich;
- optimal.
Maintaining the correct mixture ratio in the carburetor is vital for reliable engine operation.
Mixture control diagram
First, you need to start the scooter and warm it up. After setting the temperature, you should proceed according to the following algorithm:
- The mixture quality screw is tightened until it stops.
- Loosen the adjusting bolt one and a half turns counterclockwise.
- Start the scooter, tighten the screw a third.
- If the speed increases, turn it a quarter.
- We adjust until the speed stops falling.
This scheme allows you to configure all types of motorcycles.
Disassembling the block
If you need to disassemble the carburetor assembly, the next step is to remove the intermediate plate between them and the air filter. Next, you need to unscrew the bolts on the bar that holds the block together. A Keihin CVK or other model usually requires a lot of physical effort here. You will most likely need to use a T-handled screwdriver.
Next you need to disconnect the return spring. To do this, the bolts are also unscrewed in the appropriate places. The plank will easily slide off and become detached from the structure.
The carburetors are held together by a long bolt. It must also be dismantled. The block can be disassembled. The first carburetor is removed and the spring is set aside. They should not be confused in places (they differ in size). Then the outside of the housing is cleaned.
Medium and high speed tuning
The quality screw prepares the mixture ratio at idle. Failures in operation at high modes are eliminated in other ways.
After opening the throttle valve, the fuel nozzle comes into operation. Its task is to supply gasoline to the diffuser while the scooter accelerates.
An incorrectly selected nozzle leads to deviations in the composition of the fuel mixture. During power build-up, the scooter may “suffocate”, until the engine stops completely.
The correct algorithm for tuning the carburetor at high speeds:
- cleaning internal channels from debris;
- checking the fuel level in the float chamber;
- adjusting the shut-off valve (needle) stroke;
- checking the jet's nominal value.
A sign of proper operation of 2t and 4t engines is a sharp increase in speed when the gas is opened. Any deviations from the stability of engine acceleration indicate a violation of the settings.
Signs of deviation in mixture preparation
An important indicator of the quality of fuel combustion in the cylinders is the color of the spark plug. An experienced mechanic only needs to look at its condition to understand what adjustments need to be made.
There are two characteristic colors:
- A white (grey) spark plug means the mixture is lean, the moped overheats and does not produce optimal power.
- Black with soot – excess fuel, excessive consumption.
The behavior of a scooter with an incorrect fuel mixture is specific:
- abnormal reaction to the throttle;
- pops in the muffler;
- smoke content of exhaust gases;
- noticeable decrease in power characteristics;
- sudden engine stop.
A normal moped spark plug is brownish in color. There should be no carbon deposits on it, its electrodes should be clean, without traces of melting.
Cleaning
The Keihin carburetor requires careful cleaning after dismantling. To do this, you need to purchase a special tool. It should not destroy the rubber seals. There are many similar cleaners on the market. It is convenient if the product is in a bottle. Using a special tube, it will be easy to spray it throughout the entire mechanism.
Work must be carried out outdoors. Solvents contain many hazardous components. Therefore, it is highly not recommended to carry out such work indoors.
The carburetor is purged with air under pressure. If necessary, some areas can be cleaned manually using cotton swabs. If the length of the springs differs significantly (by 1.5 mm), they must be replaced.
Adjusting the fuel level
The final stage of setup is to check the gasoline level in the chamber. The procedure is simple, but the subsequent operation of the engine depends on its correctness.
The fuel collects in the float chamber. Its volume is checked using a transparent tube. The required parameter can be found in the documentation for the scooter.
The top part of the carburetor is removed. The gasoline level should be just below the low level of the cap. If the readings differ, it is necessary to adjust the stroke of the locking needle by bending the antennae. Having set the desired range, the unit is assembled, the scooter is started and allowed to run for several minutes. After this, the level is checked again.
If the value is saved, the adjustment can be considered completed. The correct setting is checked by sea trials.
Synchronization
After cleaning, the Keihin carburetor needs to be adjusted. You can start with synchronization. This is a simple procedure. But it will require a synchronizer. This device checks rarefaction.
The motorcycle must be warmed up to engine operating temperature. Next, remove the tank and filter. The synchronizer will help establish the same vacuum in the collector. The device connects to it. The engine starts.
According to the sensor readings, the valves need to be adjusted. They should respond (but not strongly) to changes in sparseness. If the synchronizer arrow does not perceive changes, the valve must be released. The process is carried out using the corresponding screws on the carburetor. First, adjust the right and left screws. Only after this can the central lever be adjusted.
Results
Despite all the difficulties and apparent complexity of the device, adjusting the carburetor on a scooter is possible both at home and in the field. It is recommended to carry it out at least once a season, especially during frosts - this will avoid flooding the candle. If your old engine starts to feel bad, adjusting the carburetor can extend its life. Although the moped will lose a little power. And yet, with the help of proper carburetor settings, you can make life much easier for yourself and your iron horse.
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