The maintenance personnel of the maintenance station conducted overhaul, replaced the electronic igniter, ignition coil, spark plug, carburetor and other parts, carried out comparative inspection, the fault could not be eliminated.
Open the ignition switch, start the engine for testing, the engine is easy to start, start the fire after idling stable operation, increase the throttle opening, do engine acceleration test, engine working speed up to the medium speed, it can not continue to rise, muffler issued a "sudden, sudden" exhaust sound, and from time to time issued the sound of blasting.
It was confirmed that the engine had poor acceleration failure. The spark plug was removed for inspection. It was found that the spark plug electrode was black, indicating that the combustible mixture was not fully burned, which was probably related to the excessive concentration of the combustible mixture.
Take off the air filter, continue to do the engine acceleration test, the engine acceleration condition is slightly improved, but the engine acceleration failure cannot be eliminated. At the same time, it is found that when the throttle opening is increased, there is obvious oil spray from the carburetor inlet, indicating that the engine has high-speed reverse injection fault.
Engine ignition system, fuel system and valve mechanism fault, can lead to engine high-speed reverse injection fault, ignition system and fuel system are used to swap parts method, comparative test, the fault can not be eliminated, can preliminarily identify engine valve mechanism fault, resulting in poor engine acceleration fault.
Open the valve chamber cover, twist off the engine inspection hole plug, use a socket wrench to slowly rotate the magneto rotor according to the working rotation direction of the magneto rotor, align the compression top dead center "T" marking line on the magneto rotor with the timing mark of the inspection hole, check and adjust the working clearance of the inlet and exhaust valve to meet the technical requirements.
Continue to slowly rotate the magneto rotor and pay attention to the action of the intake valve rocker arm. When the intake valve rocker arm presses down the intake valve with a stroke of 1mm, that is, when the intake valve opens with a stroke of 1mm, stop rotating the magneto rotor immediately and keep the original position unchanged.
Check the alignment between the marking line on the magneto rotor and the timing mark of the viewing hole to see if it meets the technical requirements. The inspection results show that the maximum ignition advance Angle "Ⅱ" marking line on the magneto rotor is about 10 mm away from the inspection hole timing mark, indicating that the engine has a problem with the valve phase, early inlet and exhaust timing, leading to the engine high speed failure.
The normal valve phase should be that the ignition advance Angle "F" marking line on the magneto rotor is aligned with the viewing hole timing mark, or the maximum ignition advance Angle "Ⅱ" marking line on the magneto rotor is aligned with the viewing hole timing mark.
Open the magneto side cover, remove the magneto rotor, electric start overrunning clutch big gear and other parts, check whether the timing gear of the crankshaft is aligned with the timing mark of the CAM gear. However, it is found that there is no regular timing mark on the timing gear group, only the CAM gear has a manual filling timing mark.
It is obvious that maintenance workers in the assembly, based on the semi-circular key on the crankshaft journal, and CAM gear timing mark alignment as the standard, assembly.
So from the timing mark, there should be no problem, but through the valve phase check has confirmed that there is a problem, decided to dismantle the engine valve mechanism.
The cylinder cover, cylinder liner and other components were removed, and the CAM gear was taken out for inspection. The problem was found by comparing with the new CAM gear. Taking the vertical line of the CAM center as the benchmark, the timing mark made manually deviated from the vertical line by two teeth, which resulted in the valve phase of the assembled engine did not meet the technical requirements and the engine could not work normally.
After inquiring, it was learned that the CAM on the CAM gear was changed after, and the timing mark on the gear was also made up.
Replace the new CAM gear, assemble the crankshaft timing gear and CAM gear according to the timing mark, install the removed parts, and check again to confirm that the engine valve phase meets the technical requirements, that is, when the intake valve opens 1 mm stroke, the maximum ignition advance Angle "Ⅱ" marking line on the magneto rotor is aligned with the timing mark of the view hole.
Start the engine and drive the motorcycle for road test. The motorcycle runs normally at high speed and the fault is removed.
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