Recently encountered a motorcycle, the owner is due to engine acceleration bad fault, to check maintenance. The whole maintenance process needs to involve the adjustment of valve phase. I have described the adjustment process for your reference.

After picking up the car, the first test run to check the engine operation, according to the symptoms of troubleshooting. Turn on the ignition switch and start the engine for inspection. The engine starts easily and the idle speed is stable. Increasing the carburetor throttle opening, engine speed test, engine working speed up to the medium speed, engine working speed will not be able to continue to improve, work speed is high and low, appear larger fluctuation, issued "spit, spit" exhaust muffler noise, release of thick black smoke, side by side shows the characteristics of combustible mixture too thick fault. The test results confirm that the engine has a bad acceleration fault.

First check the air filter, no problem found. Disconnect the air filter from the carburetor and continue the engine acceleration test to check whether there is a backinjection phenomenon when the engine is accelerating. It is confirmed that the carburetor has a serious backinjection phenomenon when the engine is accelerating, and the test results show that the carburetor backinjection causes the bad acceleration fault.

The ignition system and the engine are not working properly, which can cause carburetor backinjection. First replace the parts of the ignition system for comparative inspection, has replaced the electronic igniter, ignition coil, spark plug and other other parts for comparative inspection, carburetor backinjection phenomenon can not be eliminated, which shows that carburetor backinjection phenomenon has nothing to do with the ignition system.

Check engine with gas phase is correct, according to the rotor of the magneto job rotation direction, slowly turn the rotor of the magneto, pay attention to the action changes into the valve rocker arm, when the inlet valve rocker arm pressure inlet valve 1 mm the trip (both inlet valve open 1 mm the trip), immediately stop turning magneto rotor, and keep the original position, Check the magneto rotor on the check point on the "T" mark scribed line can timing mark alignment and engine block, check a result, magneto rotor on the check point on the "T" mark scribed line cannot be aligned to the engine block timing mark, but the ignition advance Angle on the rotor of the magneto "F" timing mark alignment marks and engine block. The inspection results showed that the opening time of the intake valve was advanced and the valve phase of the engine was incorrect.

Intake valve opening time in advance, within the engine cylinder exhaust emissions is not completely clean, is part of the residual gas, and maintain a certain pressure, when the inlet valve opens, the gas pressure inside the engine cylinder is higher than the inlet pressure and residual waste gas will be opened from the inlet valve of rush out, from the carburetor inlet, formed the jet stream.

The valve phase of the engine is not correct, usually,

First, the camshaft timing driven sprocket is not installed correctly.

Two, the camshaft of the timing driven drive sprocket connecting disk and camshaft dislocation.

Engine valve timing of inspections first, according to the rotor of the magneto job rotation direction, slowly turn the rotor of the magneto, the engine compression stroke, the magneto rotor on the check point on the "T" mark scribed line and engine block timing mark alignment, check the "O" on the camshaft timing driven sprocket whether timing tags can be aligned with the timing of the mark in the engine cylinder cover, Check result, and check the "O" on the camshaft timing driven sprocket timing tags could not aligned with the timing of the mark in the engine cylinder head, but the "O" on the camshaft timing driven sprocket timing advance the timing on the engine cylinder cover marking, inspection results show that the inlet valve opening timing is the cause of premature engine valve timing is not correct.

Newly installed correctly the camshaft timing driven sprocket, and once again check engine with gas phase is correct, according to the rotor of the magneto job rotation direction, slowly turn the rotor of the magneto, pay attention to the action changes into the valve rocker arm, when the inlet valve rocker arm under pressure when the inlet valve 1 mm (1 mm) both inlet valve open, immediately stop turning magneto rotor, and keep the original position, Check whether the top dead center (TDC) mark score on the magneto rotor can be aligned with the engine block timing mark. Check that the top dead center mark score on the magneto rotor can be aligned with the engine block timing mark. Check that the valve phase of the engine is correct.

Start the engine for acceleration test, the engine acceleration performance is obviously improved, the carburetor is still more or less a little back injection.

Carburetor oil - water level is high, can also cause carburetor slight back - injection phenomenon. Remove the carburetor from the engine, raise the working height of the oil float, and lower the level of the carburetor.

After loading the carburetor, start the engine for acceleration test, the engine acceleration is good, the muffler "spit, spit" exhaust sound disappeared, and there is no black smoke emissions. Drive the motorcycle for road test, and the motorcycle runs normally at high speed.

The failure of engine acceleration has been eliminated through inspection and confirmation.