When a four-stroke motorcycle is running, the exhaust gas from the engine should have no obvious smoke. If there is more smoke, or even smoke billowing, it indicates that the engine has a failure, and it should be repaired in time after finding out the cause.

One. Black smoke from the exhaust

(a) At this time, the mixture provided by the carburetor is too strong, the gasoline is not completely burned, and the carbon particles are discharged with the exhaust gas, for the following reasons:

1, the air filter is blocked.

2, the carburetor's compensation air passage or idle air passage is blocked.

3, the float chamber oil level is too high, so that part of the oil without atomization directly into the cylinder resulting in incomplete combustion.

4, the main measuring hole is seriously worn, so that the main nozzle injection volume increases, resulting in incomplete combustion.

5, the starting heating automatic valve is in the open position, even after the engine is preheated, the heating valve can not be automatically closed, resulting in too strong mixture.

(2) Maintenance methods

1, first check whether the air filter is blocked. For the air filter of paper filter, it is generally better to replace the filter element. If the foam filter element, the filter element should be cleaned in kerosene or non-burning detergent, after drying, apply a small amount of lubricating oil on its surface (pay attention not to apply too much, otherwise it will reduce the intake volume), and install it back after cleaning the filter wall.

2. Check the carburetor after confirming that there is no problem with the air filter. For the main pendulum throttle carburetor, compressed air is used to blow through all the holes. Check whether the position of the main oil needle is appropriate. Generally, the oil needle card should be located in the third slot. Check whether the main oil needle is excessively worn, if worn, replace the float needle seat at the same time, if the main measuring hole is seriously worn (usually when removing foreign matter with wire during maintenance, making its diameter larger), replace the main measuring hole with a new one. Check whether the height of the float is appropriate, the specific method is to turn the carburetor upside down, disassemble the float chamber, make the float tongue press the float needle valve, measure the distance between the float chamber and the top of the float, so that the float height is the same on both sides. For example, JH70 is 20mm and CG125 is 18.5mm. If it does not fit, remove the float and adjust it by pulling the float tongue with needle-nose pliers.

3, in addition, for the vacuum film carburetor such as Haumage 125, Honda CH125 should also start the heating valve yellow wire connected to the positive terminal of the battery, green wire connected to the negative terminal of the battery, about 5 minutes later, and then connect the polyethylene pipe to the fuel increment circuit, with the mouth blow, this is the time, the fuel loop is fully closed, not ventilated.

4. If it can be easily ventilated, it indicates that the automatic valve cannot close the fuel increment circuit, and the automatic starting heating valve should be replaced.

Two, exhaust blue smoke

At this time, the lubricating oil participates in combustion in the combustion chamber. Four-stroke engines use a combination of splash and pressure lubrication. The camshaft and rocker arm of the engine valve mechanism and the big head of the connecting rod are lubricated by the pressure generated by the oil pump. For the lower part of the cylinder arm, the connecting rod small and first class parts are sprayed with lubricating oil under the action of centrifugal force when the crankshaft is rotated. Because the piston makes reciprocating straight motion in the cylinder, the piston ring will form a layer of lubricating oil film on the cylinder wall, and scrape the excess oil on the cylinder wall back to the crankcase, this layer of lubricating oil film has a certain viscosity, increase the sealing of the cylinder, prevent the combustion chamber gas to the crankcase, also prevent the crankcase oil to the combustion chamber, this is normal circumstances, Four stroke engine oil consumption is small. However, in the following cases, the lubricating oil may enter the combustion chamber and cause the exhaust gas to emit blue smoke.

(A) piston component reasons

1, piston ring, piston wear serious;

2, the piston ring is carbon trapped in the ring groove, can not seal the cylinder;

3, the piston ring is broken;

4, the direction of the piston ring is reversed or the opening is in a straight line.

Where the fault is caused by 1, 2, 3 reasons, during repair, the diameter of the piston should be checked, and the piston should be replaced if the wear limit is reached. Check the gap, elasticity and light leakage of the piston ring, and replace the piston ring if the limit value is reached. For the burning of lubricating oil caused by reason 4, it must be installed according to the requirements of the piston ring during installation, the chrome plated ring (or nitriding ring) is installed in the first ring groove, the carbon steel ring is installed in the second ring, and the marked side of the ring face is upward, the outer chamfered groove is downward, the ring mouth is far from the center of the pin hole, and is evenly spaced along the circumference. The upper and lower scraping plates of the combined oil ring have no direction requirements, but the opening of the scraper should be about 20mm from the opening of the liner ring. Note that the piston ring opening deviates from the direction of the side pressure on the piston.

(2) The movement of the valve rod and the valve rod plays a guiding role, in order to ensure the flexible movement of the valve, considering the factor of thermal expansion, there is a certain coordination gap between the intake and exhaust valve rod and the valve guide. With the increase of motorcycle use time, the valve rod and valve guide will wear, when the matching gap reaches the limit, the pressure lubrication into the combustion chamber. When repairing, the diameter of the valve rod is measured with an outer diameter micrometer, if the limit value is reached, the valve is replaced, and the valve should be ground with the valve seat. Rotate the reamer to the right before measuring the valve catheter. If the reamer is rotated to the left or inserted or removed without turning, the inner surface of the catheter will be damaged. Use a dial gauge to measure the inner diameter of the valve guide and replace it if it is larger than the limit size.

Valve guides are divided into flanged and flangeless two types. Flange valve guide replacement steps are as follows:

1, the cylinder head evenly heated to 100 ° C ~150 ° C (placed in the oven), do not use the gas flamethrower for local heating, to prevent the cylinder head deformation.

2, use special tools to knock out the valve guide, be careful not to damage the cylinder head joint;

3. Apply lubricating oil on the new O-ring and install it on the valve guide;

4. Insert the new valve guide from the camshaft side before the cylinder head is cooled.

5, use the reamer to reamer the valve guide, and the reamer can not be skewed when reamer is reamer.

The method of unflanged valve guide replacement is the same as above, except that the height of the valve guide exposed to the cylinder head is measured with a caliper before removing the valve guide. Make a good record to facilitate the installation of the valve guide at the original height.

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