Carburetor Common Troubleshooting and Carburetor Cleaning and Maintenance
1. Normal Maintenance
Carburetor’s Normal maintenance is actually to maintain the cleanliness of the carburetor when it leaves the factory. This is controlled by professional carburetor manufacturers as a key indicator of carburetor quality evaluation. Various advanced equipment and processes are used in each production link. Strict control. Therefore, in order to ensure the normal use of the carburetor, we must pay attention to the normal maintenance of the carburetor: clean the carburetor regularly, keep the oil passages and air passages of the carburetor clean, and the small apertures are unobstructed. This is also very important to prolong the service life of the carburetor. Many carburetor performance failures can be solved by regularly cleaning the carburetor.
1. The carburetor is a key component in the engine, and minor changes may affect the performance of the vehicle. Therefore, during the disassembly and assembly process of the carburetor, appropriate tools should be used and the force should be moderate to prevent deformation of the parts. The disassembled parts should be neatly arranged in order to prevent missing or wrong assembly during assembly.
2. The cleaning of the carburetor should be carried out in a clean place. First wipe the outer surface of the carburetor, and use the special cleaning agent for carburetor or industrial gasoline to clean the internal parts. In addition to impurities, pay attention to cleaning the gasoline gum on the surface of the parts. The cleaned parts should be blown clean with compressed air, and cannot be wiped with cloth or paper that will produce burrs to prevent re-contamination. Blocked holes should not be opened by hard objects such as steel wires to prevent changes in the performance of the carburetor caused by changing the hole diameter. Gasoline or compressed air should be used to clean and flush out.
3. During the assembly process of the carburetor, the connecting screw of the float chamber, the connecting screw of the carburetor and the engine should not be tightened at one time, but must be tightened several times. Generally, the tightening torque is 12N.m～15N .m between. Otherwise, the joint surface will be deformed, and air leakage or oil leakage will occur. The tightening torque of measuring hole parts is generally between 1.5Nm and 3.0Nm. Excessive tightening torque will damage the thread, cause deformation of the parts, and even produce metal chips, causing secondary pollution and affecting the performance of the carburetor.
4. In the process of cleaning the carburetor, if there are many deposits in the float chamber of the carburetor, it is often caused by the failure of the gasoline filter. At this time, the gasoline filter should be checked, and if it is confirmed that it is invalid, it needs to be cleaned or replaced with a new gasoline filter.
5. If the motorcycle is not used for a long time, it is necessary to discharge the fuel in the carburetor float chamber to prevent the gasoline from colloidal deposition and condensation, which may cause the carburetor to malfunction. In addition, it should be emphasized that because the position of the idle speed adjustment screw has an important impact on the performance of motorcycle emissions, idle speed, transition, fuel consumption, etc., it is generally forbidden to rotate the idle speed air adjustment screw when cleaning the carburetor. If it is necessary to remove the idle air adjusting screw, screw the adjusting screw to the end first, remember the number of turns (accurate to 1/8 turn), and return according to the original number of turns during assembly.
Second, common faults
As a precise mechanical device, the carburetor plays an important role in the engine and can be called the “heart of the engine”. “. From a professional point of view: the failure rate of the carburetor itself is extremely low. But in actual use, the failure rate of the carburetor is often not low. There are two reasons for this:
1. Since all the working characteristics of the engine are related to the carburetor, such as acceleration, transition, fuel consumption and so on. Therefore, when judging the cause of the performance failure of the motorcycle, the failure of electrical components or other mechanical parts is often confused with the carburetor, and the carburetor is mistakenly judged as a failure of the carburetor and the carburetor is replaced. For example, the failure of the filter causes impurities to block the carburetor, and the replacement of the new carburetor eliminates the fault, but does not solve the fundamental problem.
2. The quality problems of related parts greatly shorten the service life of the carburetor. Such as the reduction of cleanliness, increased wear and tear of carburetor parts and so on.
Several common fault phenomena of motorcycle carburetors are: difficult starting, unstable idling, poor transition, insufficient power, oil leakage, high fuel consumption, etc. The above only selected the faults of the carburetor analysis. But in fact, from the perspective of the whole machine, there are many factors that cause the above-mentioned failure phenomenon. Such as difficulty in starting: the disorder of the ignition system, the change of the spark plug electrode gap, etc. will cause difficulty in starting. Such as unstable idling: In order to reduce the sound of the engine cylinder head, the motorcycle factory often adjusts the engine valve clearance too small, which leads to the deterioration of the engine intake and exhaust conditions, and the idling instability or even no idling phenomenon occurs. The user needs to analyze the fault condition of the vehicle in detail.
Difficult to start
According to the national standard, under the premise of using the carburetor to start the enrichment device correctly, the time of pedal or electric start exceeds 15 seconds If the engine still cannot keep running continuously, it is judged that it is difficult to start. The reasons for the difficulty in starting and the corresponding elimination methods are as follows.
1. There is no fuel in the carburetor float chamber
The oil inlet channel of the carburetor is blocked. The analysis and elimination steps are as follows:
Open the carburetor float chamber and check whether the oil inlet needle valve is brought down when the float falls. If the needle valve does not move with the float and is still tightly combined with the needle valve seat, it can be judged that the needle valve and the valve seat are bonded to cause the blockage of the oil inlet channel. This fault is generally caused by the condensation of gasoline gel between the needle valve and the valve seat. Can be cleaned with alcohol or acetone. Such failures often occur on motorcycles that have not been used for a long time. In particular, engine factories and motorcycle factories have not exhausted the gasoline in the carburetor float chamber after installation. In the case of a slightly longer inventory or sales period, gasoline gel condensation will occur, resulting in carburetor performance failure.
Remove the float and needle valve, connect gasoline from the carburetor inlet port, and observe the outflow of gasoline from the valve seat. Blow in from the oil inlet pipe.
In addition, a blocked oil circuit indicates that a large amount of impurities have entered the interior of the carburetor. The root cause is the failure of the gasoline filter. Therefore, when cleaning the carburetor, it is necessary to check the gasoline filter.
2. Failure of the starting thickening device
In order to improve the starting performance of the carburetor, the starting thickening device is specially set up, and the motorcycle starts There are two main structural forms of the enrichment device:
Choke mechanism: The choke mechanism is a relatively simple mechanical device generally used for straddle-type vehicles (such as CG125 motorcycles), and the choke handle can be pulled To observe whether the choke plate moves with it to judge whether it is normal or not, this device has fewer faults.
Bypass enrichment system: There are many types of bypass enrichment systems, and the most widely used are electric heating and manual bypass enrichment systems. Electrothermal bypass enrichment systems are generally used in scooters. The fault analysis and troubleshooting steps are as follows:
1) After 4 to 5 minutes after the motorcycle switch is turned on, touch the plastic shell of the electric heating starter and enrichment valve by hand. If there is heat, the circuit is normal; otherwise, it needs to be checked If the circuit at the interface of the enrichment valve is normal, it is determined that the enrichment valve is damaged and needs to be replaced.
2) During 0 to 5 minutes after removing the start-up enrichment valve and connecting the circuit, observe the movement of the enrichment valve plunger. If the enrichment valve plunger continues to extend with the spring, the enrichment valve Normal; otherwise, the PTC heating piece in the enrichment valve is damaged, and the enrichment valve assembly needs to be replaced.
3) Use compressed air to clean the enrichment channel on the carburetor body. The manual bypass enrichment system is applied to Mulan 50 and other models. The fault analysis and troubleshooting steps are as follows:
(1) Unscrew the starter valve connector, turn the thickening handle switch, and observe whether the thickening cable can drive the thickening plunger to move up and down. If it cannot be moved or the thickening plunger falls, the thickening wire is disconnected, and the thickening wire needs to be replaced.
(2) Remove the carburetor float chamber and observe whether the inner diameter of the starting foam pipe hole on the gasket of the float chamber is smaller than the outer diameter of the starting foam pipe due to expansion and contraction. If it is too small, it is necessary to replace the gasket or increase the inner diameter of the starting foam tube on the gasket, which is generally 1-2 mm larger than the outer diameter of the starting foam tube.
(3) Use compressed air to clean the enrichment channel on the carburetor body.
3. Low idle speed
The phenomenon of low idle speed is that the engine can be started but cannot run stably, and it will turn off after a while.
Remedy: adjust the carburetor plunger adjusting screw, turn it clockwise to increase the engine speed; turn it counterclockwise to reduce the engine speed. Generally, the engine speed can be adjusted to about 1500 rpm (straddle bike) and 1700 rpm (scooter).
4. Incorrect starting method
The incorrect starting method basically appears in the use of the starting thickening device, and its common incorrect starting method The options are:
Do not use the start-up thickener. This is caused by the user’s incomplete understanding of the functions of the motorcycle, because even if the starting thickening device is used at room temperature, the starting performance will be greatly improved.
The starter enricher (for choke mechanism and manual bypass enricher) is always used during start-up. When the starting enrichment system works, the engine is supplied with a very rich mixture. If the enrichment device is used all the time during the starting process, a large amount of rich mixture entering the cylinder will “drown” the engine, making it difficult to start.
The correct way to use the enrichment device is: if the engine still cannot run after starting 3 to 4 times, close the enrichment device, and turn the throttle handle slightly to make the carburetor plunger rise and then start again.
Idle speed instability
Idle speed instability phenomenon: After the engine has been running for several minutes to warm up, the idle speed of the engine fluctuates more than ±100 rpm. unstable.
The reason for the unstable idle speed: when the oil passage or air passage of the carburetor idle speed system is blocked or leaked, the oil supply of the idle speed oil system appears lean or rich, resulting in unstable idle speed of the engine .
1. The idle speed measuring hole is partially blocked
Reason: The idle speed measuring hole is partially blocked, which makes the oil supply in the idle speed state lean and causes the idle speed to be unstable. Appear.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
2. The position of the idle speed adjustment screw (commonly known as “wind needle”) changes
The function of the idle speed adjustment screw is to change the idle speed oil by adjusting the idle speed adjustment screw The flow section of the channel or the air channel makes the carburetor idle oil supply reach the ideal state. The idle speed adjustment screw can be divided into two types: oil adjustment (such as CG125 carburetor) and air adjustment (such as Mulan 50 carburetor).
For professional carburetor manufacturers: Since the idle speed adjustment screw has a great influence on the performance of the engine, the idle speed adjustment screw of the carburetor has been strictly tested and adjusted to the best position before leaving the factory. . Therefore, it is generally forbidden for the user to adjust the idle speed adjusting screw by himself. After a long period of use, the idle speed adjustment screw can only be adjusted if the position of the idle speed adjustment screw does change and causes adverse consequences. There are two ways to find the best position for the idle adjustment screw:
(1), the best adjustment method
First fix the plunger to the Accumulate the engine speed with a slightly higher idle speed, rotate the idle speed adjustment screw left and right to find the maximum speed at the position of the plunger, adjust the plunger adjustment screw slightly to reduce the engine speed and then find the maximum speed, and so on, until a certain plunger The maximum speed at the position is equal to the standard idle speed of the whole vehicle. For a four-stroke engine, sometimes the CO concentration is still very high after the best adjustment is done. In this case, the Paris adjustment method can be appropriately used.
(2), Paris adjustment method
The Paris adjustment method is carried out on the basis of the best adjustment method. Turn the adjusting screw a little in the direction of making the mixture thinner (only 1/8 of a turn is allowed at most), at this time, the speed should be reduced, and then increase the plunger to restore it to the original speed. As a result of the adjustment, the HC value is slightly increased and the CO value is decreased. The principle is that HC cannot rise too much, and CO can be slightly lower than the standard. If the results of the Paris adjustment method make CO meet the standard, but make the HC exceed the standard is not allowed. If CO and HC cannot meet the standards at the same time, it means that the carburetor cannot meet the emission requirements when the conditions do not change. It can also be seen here that limiting CO and HC can ensure the rationality of the adjustment. Otherwise, the CO will be lowered blindly, the result will be too high HC, and the combustion will be in an extremely unreasonable state.
If the best adjustment method is used but the emission reaches the standard, it is better not to use the Paris adjustment method. If the HC meets the standard but the CO exceeds the standard, the Paris adjustment method can be used appropriately. If the Paris adjustment method cannot make CO and HC at the same time If the standard is met, the carburetor and ignition system need to be checked.
3. The gasket or rubber ring connecting the carburetor and the intake pipe of the engine is damaged
If the connecting gasket or rubber ring is damaged, air leakage will occur. The extra air enters the engine, making the fuel supply lean at idle speed, resulting in unstable idle speed.
Remedy: replace the connection gasket or rubber ring.
4. Loose connecting bolts between carburetor and engine intake pipe
If the connecting bolts are loose, air leakage will also occur. Remedy: Tighten it.
One thing to point out is that the carburetors used on most scooters today are equipped with an electrically heated bypass enrichment system. Under the action of this system, the idle speed of the motorcycle is high after starting (up to 2200-2300 rpm), and after the electric heating bypass enrichment system is turned off for 4-5 minutes, the idle speed of the engine returns to 1500. rev/min. This is a normal phenomenon and does not belong to the “unstable idle” fault. Please be careful not to misjudge.
Poor transition
When the motorcycle is accelerating from the start, the carburetor idle oil supply gradually decreases and transitions to the main oil supply Increasing. In order to make the oil supply connection between the idle oil system and the main oil system smooth, a transition oil system is set up to ensure the smoothness of the motorcycle’s starting process. The phenomenon of poor transition: During the start-up acceleration process, the engine speed fluctuates greatly or stalls as the throttle is opened.
The reasons and troubleshooting methods for poor transition are as follows:
1. Idle speed measuring hole, idle speed oil circuit, main measuring hole, transition hole part Blockage
Cause: Partial blockage of idle speed measuring hole, idle speed oil circuit, main measuring hole and transition hole makes the oil supply of each relevant oil system of the carburetor lean, resulting in poor transition.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
2. The foam pipe is blocked
Reason: The function of the carburetor foam pipe is to promote the mixing of gasoline and air, and the foam holes on the foam pipe are blocked. After the impurities are blocked, the mixing effect of gasoline and air is reduced, and the atomization quality is reduced, resulting in poor transition.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
3. Poor idle speed adjustment
Reason: During the transition process, the oil supply of the carburetor mainly comes from the idle speed oil system. If the idle speed adjustment is improper, it will affect the Transition performance.
Remedy: Adjust according to the above-mentioned adjustment method of idle speed adjusting screw.
Insufficient power
The lack of power mainly reflects the acceleration performance and high-speed performance of the motorcycle.
There are two indicators for motorcycle acceleration evaluation: start acceleration and overtaking acceleration. Its performance indicators vary with different models and displacements, and the detection methods (such as the timing of shifting gears and grasping the speed of opening the accelerator) are not easy for users to grasp. Because different users have great differences in the speed of throttle control, the feeling of acceleration performance is also different. Therefore, when the user feels that the acceleration is not good, it is best to go to a professional maintenance point for diagnosis. Users can preliminarily judge whether their motorcycle has insufficient power through the following phenomena. The acceleration process is noticeably slower and less dynamic than before.
The maximum speed drops, the vehicle “rushes” at high speed, and the exhaust pipe is shot.
The reasons for the lack of power and the troubleshooting methods are as follows:
1. The idle speed orifice is blocked
Reason: The blockage of the idle speed orifice will cause the oil supply of the carburetor to be too thin, resulting in insufficient power.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
2. Idle oil passage, air passage or main oil passage, air passage blocked
Reason: idle oil passage, air passage or main oil passage, Blockage of the air passage will cause the oil supply to the carburetor to be too lean or too rich, resulting in insufficient power.
Exclusion method: same as above.
3. The start-up enrichment device works abnormally
Reason: This fault mainly occurs on the bypass enrichment device. The failure of the electric heating bypass enrichment device or the failure of the starting plunger during the extension process of the starting plunger or the poor return of the starting plunger of the manual bypass enrichment device will cause the starting plunger to not fall to the bottom, resulting in poor operation of the engine if the mixture is too rich.
Remedy: – For the carburetor equipped with the electric heating start enrichment device: the electric heating start enrichment valve needs to be replaced. – For vehicles equipped with a manual thickening device: Generally, it is caused by the excessive friction between the thickening cable and its outer casing after long-term use, and it can be solved by applying butter or other lubricating oil on the surface of the thickening cable.
4. The accelerator pump device is not smooth or blocked (for the carburetor equipped with the accelerator pump device, such as CB125 motorcycle carburetor)
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When the motorcycle accelerates, due to the fast lifting speed of the plunger, the fuel supply lag and lean phenomenon will occur at this time. To this end, an acceleration pump device is set on the carburetor for some models: at the moment of acceleration, an additional part of the oil is supplied to meet the demand of the engine, improving the responsiveness of acceleration. Reason: The oil passage of the accelerator pump is blocked or the diaphragm of the accelerator pump fails.
Remedy: If the oil passage of the accelerator pump is blocked, use compressed air to clean the oil passage of the accelerator pump; if the diaphragm of the accelerator pump fails, the diaphragm of the accelerator pump needs to be replaced.
Oil Leaks
The carburetor oil intake system is a dynamically balanced system. Under the action of gasoline buoyancy in the float chamber, the float drives the needle valve to continuously adjust the gap between the needle valve and the valve seat to control the oil intake, so that the oil level in the float chamber of the motorcycle remains dynamic and stable under various working conditions. The phenomenon of oil leakage in the carburetor is caused by the destruction of the above-mentioned balance system. Carburetor oil leakage not only increases fuel consumption and affects vehicle performance, but more importantly, causes greater harm to vehicle safety. need to be ruled out in time. Causes and elimination methods of oil leakage from carburetor:
1. Foreign matter adhered to the contact surface of needle valve and valve seat
Reason: needle valve and valve seat It is to control the oil intake, and its tightness requirements are strict, and the contact surface finish is high. If foreign matter is attached to the contact surface, the needle valve and the valve seat will not be tightly sealed, resulting in oil leakage. Foreign matter mainly refers to impurities and coagulant in gasoline. Therefore, to avoid such failures, users should pay attention to regularly cleaning the gasoline filter and using good-quality gasoline.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
2. Needle valve wear
Cause:
1) Needle valve is in use Due to the long-term erosion of the impurities contained in the gasoline and the contact with the valve seat, it is worn;
2) The two ends of the float float are adjusted unbalanced, which drives the needle valve to be worn by lateral force. The needle valve is worn and the valve seat is not tightly sealed and oil leaks.
Exclusion method:
1) Replace the needle valve, and users should pay attention to regularly cleaning the gasoline filter and using good quality gasoline;
2) Replace the needle valve, and at the same time adjust the two ends of the float to be on the same level.
3. Float card issuance
Reason:
1) The float is swelled and deformed by long-term immersion in gasoline Contact with the wall of the float chamber;
2) The gap between the float pin and the float pin hole of the body expands after long-term friction, causing the float to contact the wall of the float chamber. The float hairpin prevents the needle valve from returning, resulting in oil leakage.
Remedy:
1) If the float is deformed, replace the float;
2) If the outer diameter of the float pin becomes smaller Then replace the float pin. If the wear of the float pin hole of the body becomes larger, only the carburetor assembly can be replaced.
4. The float is damaged or immersed in gasoline
Reason: If the float is damaged or immersed in gasoline, the weight and buoyancy of the float will change, resulting in the rise of the oil level , causing an oil leak.
Remedy: Replace the float.
High fuel consumption
Fuel consumption is an important performance indicator that motorcycle users care about most, and it is also an important performance indicator of motorcycles. The carburetor is a key part of the motorcycle fuel supply system, and whether the carburetor is in good condition has a very important impact on the fuel consumption of the vehicle. Reducing fuel consumption is also a constant pursuit of carburetor manufacturers.
Generally, the actual driving fuel consumption rule is: the two-stroke is higher than the four-stroke, the large displacement is higher than the small displacement, and the automatic clutch is higher than the manual clutch. In addition, the structure of the engine is different, and the fuel consumption is also different. The specific value should be determined according to the specific model. For the more common models in China: the fuel consumption of two-stroke 50 vehicles is about 3L/100km, the fuel consumption of four-stroke 70-100 vehicles is below 2L/100km, the fuel consumption of four-stroke 125 vehicles is about 2L/100km, and the four-stroke 70-125 The fuel consumption of the scooter is around 3.0L/100km. Based on this, users can generally judge whether their car has high fuel consumption.
Causes of high fuel consumption and troubleshooting methods:
1. Carburetor oil leakage
See above for the causes and troubleshooting methods of oil leaks.
2. Partial blockage of the air orifices of each oil system
Reason: Partial blockage of the air orifices of each oil system will cause the carburetor to supply rich oil lead to increased fuel consumption.
Exclusion method: Just follow the above-mentioned carburetor cleaning method.
3. The start-up enrichment device is not closed tightly
The reasons and elimination methods of the start-up enrichment device are not closed tightly.
4. The outer diameter of the main oil needle is reduced after wear, and the wear of the main nozzle hole is too large
Reason: the above parts are in use during the use Due to the long-term wear and tear of the impurities contained in the gasoline at high speed, the outer diameter of the main oil needle is reduced, and the main nozzle hole is too large, resulting in an increase in fuel supply and an increase in fuel consumption.
Remedy: replace with a new measuring hole.
