Carburetor Mikuni VM 26
The Mikuni VM 26 carburetor is very common: it is installed on many pit bikes as standard.
For example, on a Pitster with a Zongshen 160 engine. The carburetor is very simple and does not differ much from the same VM 22 structurally. Naturally, there is a difference in the diffuser, this goes without saying: as you can see, even judging by the name, it is 26 mm.
You won't have any problems with the installation.
, it attaches extremely simply. No adapters or other design complications. Just screw it to the pipe with two M 6 bolts - and it’s in place.
The carburetor is based on a conventional round valve
, so no surprises or complications: “Simplicity is the key to reliability” - this, one might say, is the motto of this carburetor. Please note that you will not find an adjustment screw either on the right or on the left, only perhaps the idle speed screw, but the adjustment screw is located at the bottom.
Of course, this is not very convenient, but you get used to everything, especially since you don’t need to adjust the carburetor so often: a couple of times a year you can suffer a little. As you can see, the adjusting screw is located closer to the inlet pipe, and this can only mean one thing - the adjustment of the fuel-air mixture is carried out using more or less fuel supply to the air. We tighten the screw - we lean the mixture, unscrew it - we enrich it. Nothing complicated.
Suction
to facilitate starting in the cold season, it is carried out by means of an air damper and a flag that controls it.
The damper works very simply: we shut off the air supply - we enrich the mixture, since there is less air and more gasoline.
The damper has three operating modes
, and, in turn, the control flag also has three fixed positions.
First position
– this is when the air damper is completely open and nothing prevents the passage of air; the flag is raised up.
Second position
designed to warm up the engine, the choke closes approximately 70% of the air flow, and the mixture becomes rich, there should be no problems with starting. In this position, you should start it early in the morning, when it is still very cold, or after a long period of inactivity. The flag should be in the middle fixed position.
Third position
– extreme bottom. Accordingly, the flag is in the lower fixed position, and the damper almost completely blocks the air flow. This position is required when you need to create a very rich mixture, for example, for starting in sub-zero temperatures.
The carburetor will work well in combination with the YX 150 and YX 160 engines.
Result:
The carburetor is quite cheap, but the engine runs properly and smoothly. Naturally, you won’t achieve any kind of super explosive dynamics, but smooth operation and ease of maintenance of the carburetor - very much so.
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Mikuni carburetor
In this review, we would like to tell you about the Mikuni carburetor, namely, the VM 22 model. This device is produced by one of the Japanese companies, which leads to initial thoughts that the mechanism is quite reliable. And indeed, as practice shows, Mikuni carburetors can serve you for quite a long time and not bother you with constant breakdowns during operation. The secret of such reliability lies in an indecently simple device. Some might say that such a simple design simply cannot be reliable, and they would be wrong.
Many owners of motorcycles on which a Mikuni carburetor was installed talked about how good this unit is. By the way, it is also worth saying that the Mikuni VM 22 model is usually installed on motorcycles with an engine with a volume of 125 cm3. Among such motorcycles are the Honda CBR 125R, Yamaha YBR 125 and other motorcycles from Japanese manufacturers.
Carburetor Mikuni VM 22
Well, there’s nothing complicated about it at all: it’s like a brick. You can only break something out of stupidity or from a “great” mind.
It attaches in a classic way
, without any adapters or other nonsense, just firmly to the pipe with two M6 bolts.
There are no bells and whistles with the damper either.
. A conventional round throttle valve: a design that has not left the assembly line for almost 80 years. In general, the theory of simplicity and reliability of bricks works again)
But despite its simplicity, you should not think that this carburetor is bad! Vice versa! This is the best carburetor that you can and should install on your 125 cc pit bike!
And what is noteworthy is that there is not a rather primitive air damper operating in three positions, but a full-fledged suction
, which has two positions.
First position
– the flag is lowered down, while the fuel channel is CLOSED!
Second position
– the flag is raised. It is in this position that the fuel channel is OPEN!
In the raised position of the flag, we open an additional fuel channel, thereby creating a rich mixture.
This is very helpful when starting the engine in the cold season: you just have to lift the flag, and literally within 2-3 times the engine begins to purr. In the warm season, when starting, for example, in the morning, you need to raise the flag, pull the kick 2 times: the engine, as a rule, grabs and immediately stalls, after which we lower the flag and calmly start it. It turns out to be a kind of swap mode. But in sub-zero temperatures, the engine starts with the flag raised and will continue to do so until it warms up completely, after which it either begins to run unevenly or stalls completely. In general, it choke from excess fuel and too little air.
But in this suction system one stable unpleasant feature has been noticed. Very often, after, for example, driving through mud, the suction valve begins to jam when opening or closing. You shouldn’t be afraid of this: the flag itself gets stuck in the place of the restrictive plate, where it is in direct contact with it.
To avoid jamming, simply keep this unit clean and tidy, or even better, sometimes lubricate it with a small amount of grease, such as lithol.
But despite all the advantages and good work, there is one design idiocy here, namely the location of the adjusting screw.
The Japanese installed this carburetor on the lower vertical bars, and it was possible to get to the screw. Here is an example of such a motor.
Now let's look at how all this is located on the pit bike.
Maybe we don’t understand something, but what kind of tool can we get into the centimeter distance between the hot cylinder and the adjusting screw? How to regulate it? By the power of thought?
In general, without getting burns on your hands and there’s nothing else you can do to get there except with a head from a set of keys, fortunately you don’t have to do this very often.
By the way, the adjusting screw is responsible for more or less fuel supply to the mixture. Accordingly, if we tighten the screw, we lean the mixture; if we unscrew it, we enrich it.
As mentioned above, you only need to install this carburetor on 125 engines, although from the factory it is priced at 140, but this is more than a crazy idea: it is stupidly small for a 140 engine, but on 125 it works just fine).
Result:
in terms of characteristics, simplicity and price, this is the best carburetor that can be installed on 125-110 engines. Yes, there is a point where adjustments are inconvenient, but you have to come to terms with this fact. But this is a truly eternal carburetor, which is very difficult to render inoperative.
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Operating principle and features
And now, we move on to the most important thing - the operating principle of this carburetor. As mentioned above, the Mikuni MV 22 carburetor model has a unique air damper of its kind. Thanks to the existing two positions, it is possible to regulate the amount of enriched mixture entering the chamber of the internal combustion engine. Let's look at these two provisions in a little more detail.
Standard position (lowered flag) - in this position, the additional channel for the supply of the enriched mixture is closed, i.e. The engine receives only the fuel supplied directly by the carburetor.
Open channel position - it is in this position, when the flag is raised up, that additional fuel enters the combustion chamber through the carburetor.
Setting up carburetors using the example of Mikuni VM26 and Yoshimura Mikuni TM-MJN 22/24/26
The air-fuel mixture is the ratio of fuel to air. By increasing the amount of air, we reduce the proportion of fuel; the air-fuel mixture becomes lean. By reducing the amount of air, we increase the proportion of fuel, the air-fuel mixture becomes richer. For proper engine operation, it is necessary to establish the optimal air-fuel ratio for it by correctly setting the carburetor.
The following factors influence the setting: air density, changes in temperature and humidity, pressure (altitude above sea level). The following table shows the behavior of the air-fuel mixture depending on changes in the surrounding weather:
Symptoms of a rich mixture:
Symptoms of a lean mixture:
What is a carburetor and what is its main task?
Before discussing the most interesting new products that you may consider installing on your motorcycle, you need to understand what a carburetor is.
So, a carburetor is a special mechanism that is a component of the power supply system of an internal combustion engine. The main task performed by the carburetor is mixing fuel with air and regulating the amount of combustible mixture entering the engine of a car or motorcycle. Today we can rarely see a carburetor on a car, since with the development of technology a more practical and efficient mechanism has appeared - an injector. However, the carburetor system on a motorcycle is a completely familiar story. The same Mikuni carburetor is found quite often.
When choosing a motorcycle, many people consciously choose a motorcycle with a carburetor fuel supply system. Although the fuel injector is a more modern mechanism, which has some advantages for the average motorcyclist, the carburetor is still in service. As a rule, the carburetor system is chosen by bikers who are fond of stunt riding, where the injector does not allow full control over the motorcycle.
Operating principle of VM26 and TM-MJN22/24/26 carburetors
Fig.1 Operation of the propeller (AS)
A needle is installed in the throttle valve, which regulates the amount of gasoline supplied to the main channel to mix it with air. The needle affects the quality of the mixture in the throttle opening range from 1/8 to fully open. VM type carburetors have a regular needle with five grooves for adjustment (Fig. 2).
Fig.3 Differences between needle and tube
The influence of all carburetor systems on the qualitative composition of the mixture depending on the degree of throttle opening on the TM-MJN24 can be seen in Figure 4. This relationship is also valid for VM26 carburetors.
Fig. 4 The influence of different TM-MJN24 carburetor systems on the quality of the mixture
Installation Guide
Important! Adjust the carburetor on a warm engine, and then do a test drive. Use a spark plug with a heat rating recommended by the engine manufacturer.
The fuel mixture is the ratio of gasoline and air. By increasing the amount of air and decreasing the proportion of fuel, we make the air-fuel mixture leaner. By reducing the amount of air and increasing the proportion of fuel, we make the mixture richer. For all engine operating modes, it is necessary to adjust the optimal ratio of gasoline and air.
The mixture ratio in these positions can be adjusted by replacing the main jet. The higher the main jet number, the richer the mixture becomes. Depending on the engine and muffler parameters, select the most suitable jet to achieve maximum speed.
The mixture ratio at these throttle positions can be adjusted by placing the E-ring at different needle positions. The air-fuel mixture becomes richer when the E-ring is moved down from the 1st to the 5th groove.
The propeller regulates the air flow while the engine is spinning at low speed (idling).
Loosen the idle screw (at the throttle body) until you get a stable idle speed. Again, adjust the propeller position to obtain high rpm.
Check if you have selected the correct auxiliary jet. The engine should accelerate smoothly from idle to low speed.
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