Motorcycle carburetor

Motorcycle carburetor looks very complicated, but as long as you master some principles, you can adjust the motorcycle to the best condition. All carburetors work under the basic principle of atmospheric pressure. Atmospheric pressure is a powerful force that exerts pressure on everything. Slightly different, but usually there is a pressure of 15 pounds per square inch. This means that the atmospheric pressure is 0/5 pound per square inch/kloc. By changing the atmospheric pressure in the engine and carburetor, we can change the pressure to make fuel and air flow through the carburetor.

Atmospheric pressure will spread from high pressure to low pressure. When the piston of a two-stroke engine is at the top dead center (or when the piston of a four-stroke engine is at the bottom dead center), a low pressure will be formed below the piston in the crankcase (above the piston of a four-stroke engine). At the same time, this low pressure will also cause low pressure in the carburetor. Because the pressure outside the engine and carburetor is relatively high, air will rush into the carburetor and enter the engine until the pressure is balanced. The air flowing through the carburetor will push the fuel, which will be mixed with the air.

Inside the carburetor is a throat, as shown in figure 1. The throat is a constricted part of the carburetor, which forces the air to pass through at an accelerated speed. The sudden narrowing of the river can explain what happened in the carburetor. The river will accelerate as it approaches the narrow bank, and even faster if the bank continues to narrow. The same thing happened to the carburetor. The accelerated airflow will cause the atmospheric pressure in the carburetor to drop. The faster the air flows, the lower the pressure in the carburetor. By placing a tube in the throat, we can use low pressure to mix fuel into the air flow.

Most motorcycle carburetor passages are controlled by throttle position rather than engine speed. Most motorcycle carburetors have five main regulating systems. These regulating systems interact with each other. They are:

Idle channel

Idle measuring hole

Main nozzle and oil needle

Main measuring hole

Choke flow channel

The idle channel has two adjustable parts, as shown in Figure 2. Throttle air screw and idle metering hole.

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zhangjt932

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Principle of Off-line #2 Motorcycle Carburetor (2)

The air screw can be installed at the rear or front of the carburetor. If the air screw is located at the back, it is used to adjust the amount of air entering the throttle system. If the air screw is screwed in, it will reduce the air volume and increase the rich mixture. If it is screwed out, it will open more channels and let more air into the channels, resulting in dilution of the mixture. If the air screw is located in the front, it regulates the fuel supply. If it screws in, the mixture will be diluted; if it screws out, the mixture will be concentrated. If the pneumatic screw must be rotated more than two times to obtain the best idle speed and performance, the smaller or larger idle speed measuring hole must be replaced.

When the throttle opening is low, the idle metering hole is the part that supplies the most fuel. It has a small hole to restrict the flow of fuel. Both idle air screw and idle throttle affect the vaporization from idle speed to about 1/4 throttle opening.

The plunger affects vaporization between 1/8 and 1/2 throttle opening. Especially, the effect (vaporization) is between 1/8 and 1/4 (throttle opening), but it has little effect between 1/4 and 1/2 (throttle opening). Plunger has different sizes and specifications, and the specifications are determined by its back cut size, as shown in Figure 3. The larger the incision, the thinner the mixture (because more air is allowed to pass through), and the smaller the incision, the thicker the mixture. There is a number on the piston to indicate the degree of cutting. If there is a number 3 on the plunger, it means that it has a gap of 3 mm. When that number is 1, it means that there is a gap of 1 mm (the mixture will be thicker than the number 3).

The oil needle and the main nozzle affect the vaporization from 1/4 to 3/4 throttle opening. The oil needle is a long conical rod, which controls the amount of fuel that can be sucked into the carburetor throat. The thinner the cone, the thicker the mixture. The thicker the cone, the thinner the mixture, because the thicker cone will not allow more fuel to enter the carburetor as the thinner cone does. The design of the cone is very accurate, and it can provide different mixture under different throttle opening. The top of the oil needle is provided with a plurality of grooves. A clamp is installed on one of these grooves to prevent it from falling off or shifting from the plunger. The position of the fixture can be changed to make the engine run richer or leaner (mixture state), Figure 4. If the engine needs lean mixture, the fixture should be moved to a higher position. This will make the needle valve enter the main nozzle deeper, thus reducing the amount of fuel flowing through the main nozzle. If the jig is lowered and the oil needle is lifted, the mixture will be thicker.

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zhangjt932

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From Guangdong

Principle of Off-line #3 Motorcycle Carburetor (3)

The main nozzle is where the oil needle slides in and out. Depending on the inner diameter of the main nozzle, it will affect the oil needle. The main nozzle and the oil needle work together to control the fuel flow within the range of 3/4 to 1/8 (throttle opening). Most of the adjustments in this range are for the oil needle, not for the main nozzle.

The main orifice controls the fuel flow from 3/4 throttle opening to full throttle opening, as shown in Figure 5. Once the throttle opening reaches a certain level, the oil needle is pulled out of the main nozzle to a sufficient height, and at this time, the main metering hole begins to adjust the fuel flow. The main metering holes are different in size, and the larger holes can let more fuel pass through (richer mixture). The hole with larger number on the main metering hole has richer air/fuel mixture than the hole with smaller number.

Choke system is used to start the cooler. Due to condensation in a cold engine, the fuel will stick to the cylinder wall, so the mixture is too thin to start the engine. The choke system will add fuel to the engine to compensate for the fuel condensed on the cylinder wall. Once the engine is warmed up, condensation is not a problem, and the choke is no longer needed.

The air/fuel mixture must be changed to meet the needs of the engine. The ideal air-fuel ratio is 14.7 g air/1 g fuel. This ideal ratio can only be achieved in a short time when the engine is running. Due to incomplete fuel vaporization at low speed or additional requirements for fuel at high speed, the air-fuel ratio is usually relatively rich in actual operation. Chart 6 shows the actual air-fuel ratio at any specific throttle opening.

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zhangjt932

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Principle and Adjustment of Off-line #4 Motorcycle Carburetor (4)

Once you know the basic principle, troubleshooting carburetor is a simple matter. The first step is to find out what's wrong with the engine.

Figure 7 shows various channels and which channels are most influenced by each component. It must be remembered that the working condition of carburetor is determined by throttle position rather than engine speed. If there is a problem with the engine at low speed (idling to 1/4 throttle opening), there may be a problem with the throttle or plunger. If the engine has a problem between 1/4 and 3/4 throttle opening, then the oil needle and the main nozzle (probably the oil needle) may be faulty. If the engine runs between 3/4 throttle opening and full throttle opening, it is likely that the main metering hole is out of order.

When adjusting the carburetor, stick an adhesive tape on the throttle handle seat. Stick another tape on the throttle handle and draw a straight line from one tape to the other (when the throttle is idling). When these two lines are aligned, the engine will run at idle speed. Now fully open the throttle and draw a straight line from the line segment on the throttle handle. In this step, there should be two wires on the throttle handle seat and one on the throttle handle. Now find the midpoint of the two line segments on the base of the throttle handle. Make a sign, which will be displayed when the throttle is half open. Divide the interval upward again until idle speed, 1/4, 1/2, 3/4, and the full throttle position is determined. These lines will be used to quickly find the accurate throttle opening in the adjustment process.

Clean the air filter and warm the car.

When the motorcycle is idling, the idle channel can be adjusted and then put into trial operation. If the engine is not running well, it can only maintain idle speed, and the air-fuel ratio can be changed by screwing in or out the screw of the idle speed measuring hole. If the adjusting screw is behind the carburetor (like most off-road vehicles), screwing it out will dilute the mixture, and screwing it in will thicken the mixture. If the adjusting screw is in front of the carburetor (like most street cars), the situation is just the opposite. If it is not important for the screw to rotate between one turn and two and a half turns, the idle metering hole must be made larger or smaller. When adjusting the idle screw, turn 1/4 turns at a time, and try the motorcycle between adjustments. Adjust the idle screw until the motorcycle does not feel sluggish from idle to running.

After adjusting the idle metering hole, accelerate the shift until the throttle is in the half-open position. (An upward gentle slope is the best place) After running for a few minutes with the throttle half open, quickly grab the clutch and turn off the engine. Don't let the engine idle or slide when the clutch is not disengaged. Remove the spark plug and check its color. It should be light brown. (For more information about spark plugs, please visit/motooff/moto/mcycle/plug2/plug2.htm). If it turns white, lower the clamp on the oil needle to thicken the air/fuel mixture. If it is dark brown or black, lift the clamp on the oil needle to dilute the air/fuel mixture.

Once the oil needle is set, the shift will be accelerated until the throttle is in the full open position. Grasp the clutch quickly and turn off the engine. Don't let the engine idle or slide when the clutch is not disengaged. Check the color of the spark plug. If it turns white, it means that the air-fuel mixture is too thin, and a relatively large main metering hole must be installed. If it is black or dark brown, it means that the air/fuel mixture is too rich and a relatively small main metering hole must be installed. When replacing the measuring hole, change one specification at a time, try it after each replacement, and check the color of the spark plug after each operation. Ignoring this operation will cause engine failure.

There are still many things to be done to truly and thoroughly adjust the carburetor, but the above steps will make you really close to (adjust the carburetor) and improve engine performance. For most contestants, these simple steps are necessary. If your name is Ricky, Ezra, or Kevin, you will participate in the semi-finals and your mechanic will know what to do.

Height, humidity and temperature

Even if the adjustment is completed and the motorcycle runs well, there are still many factors that will change the performance of the engine. Altitude, temperature and humidity are important factors that affect the running condition of the engine. When the air is cold, the air density increases. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner (mixture state) (because of all those extra air molecules) and more fuel must be added to compensate. When the temperature is hot, the engine will run in a rich state (because there are fewer air molecules), and the demand for fuel will decrease. When the temperature reaches 90 degrees Fahrenheit, the engine adjusted to 32 degrees Fahrenheit may not work well.

Because the air molecules decrease as the altitude increases, the altitude will affect the adjustment of the engine. Because less air enters the carburetor. A motorcycle that runs well at sea level will run in a thick mixture when it reaches an altitude of 10000 feet.

Humidity is the amount of water in the air. When the humidity increases, the mixture will thicken. A motorcycle that runs well in dry air in the morning will run in a state of rich mixture with the increase of air humidity the next day.

When the temperature and altitude change, the correction factor is sometimes used to find the correct carburetor setting. The chart in Figure 8 shows Kawasaki's typical correction coefficient chart. In order to use this chart, adjust the carburetor and record the specifications of the throttle valve and the main orifice. Measure the correct temperature and follow the chart to the right until you find the correct height. Go straight down from this point until you find the correct correction coefficient. Take Figure 8 as an example. The temperature is 90 degrees Fahrenheit and the altitude is 3200 feet. The correction factor will be 0.92. In order to find the corrected main orifice and idle orifice, multiply the correction coefficient by each nozzle specification. Multiply the main hole size 350 by 0.92, and the new main hole size will be 322. The idle hole size is 40 times 0.92, and the idle hole size will be 36.8.

[Last edited by zhangjt932 on 2005- 12-5 15:47]

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2005- 12-5 15:44 Just look at the principle of this man's motorcycle carburetor.

zhangjt932

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Principle and Adjustment of Off-line #5 Motorcycle Carburetor (5)

The correction factor can also be used to find the correct setting of the main nozzle, oil needle and air screw. Using the chart in Figure 8, the correction coefficient is determined. Then use the table in Figure 9 to decide how to adjust the main nozzle, oil needle and air screw.

Now you have mastered it. Carburetor theory 10 1. Take what you have learned in this course and adjust your motorcycle. Knowledge is power. Power is everything. If you have any questions, please visit my website in www.motocross.com/motoprof or email me in motoprof@motocross.com. Keep it until next month.

DougJenks reserves all rights.

/motorcycle professor

Date of establishment: 2001September 10.

Age47 was translated on June165438+1October 65438+April Thursday, 2002.

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Cars are all single carburetor, why not motorcycles?

The old carburetor cars are all 1 carburetor, 4 cylinders. Why is a motorcycle with a carburetor in one cylinder? What are the benefits?

In the intake process of multi-cylinder internal combustion engine, there is a phenomenon that two cylinders (or more cylinders) intake air, which is called "gas grabbing phenomenon". The result of "gas grabbing" is that the two cylinders restrict each other and neither cylinder can fully intake air. Due to the large air velocity and inertia, this situation is more prominent at high speed and large inflation. Parallel operation of carburetors can reduce the phenomenon of "gas grabbing", and at the same time, due to the reduction of air flow distance, the charging capacity of internal combustion engine can be increased, making the intake of each cylinder more uniform. The power and torque of internal combustion engine can be improved correspondingly compared with that of single-chamber carburetor. The more cylinders, the higher the speed, and the more obvious the effect of improving inflation.

The above is a passage from beijing institute of technology press's Principle, Structure and Adjustment of Automobile Carburetors.

The landlord said that the maximum engine speed does not exceed 6000 rpm, and some even do not exceed 4000 rpm. Therefore, the single-cavity carburetor is selected from the cost of manufacturing process. However, the maximum speed of motorcycle multi-cylinder engine is rarely lower than 10000 rpm, so multi-cylinder motorcycle chooses multi-cavity parallel carburetor.

August 26, 200613:11Just look at this man who accidentally ran 4500 kilometers [Liaoning-Jiangxi ~ add new photos]

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I think your theory is so clear! ! !

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Excuse me, prawns, how can I adjust the carburetor if I go from plain to high altitude? Is it idle speed adjustment or liquid level adjustment? Can you introduce the specific adjustment?

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2007-9-30 19: 16 depends on this person's eight thousand miles! ! (My wife and I's motorcycle trip) Qinghai Lake part

& lt& lt[ 1] [2] [3] [4] [5]>& gt

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