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

After receiving the car, the first test run to check the engine operation, troubleshooting according to the symptoms. Open the ignition switch and start the engine for inspection. The engine is easy to start and the idle running 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 results of the inspection confirmed that the engine had a failure of acceleration.

First check the air filter and no problem was found. Disconnect the connection between the air filter and the carburetor and continue the engine acceleration test to check whether there is backjet when the engine accelerates. It was confirmed that there was serious backjet in the carburetor during engine acceleration, and the results showed that it was the backjet in the carburetor that caused the poor acceleration of the engine.

Ignition system and engine failure, can not work normally, can cause the carburetor back jet phenomenon. First, the parts of the ignition system were replaced for comparative inspection, and then electronic igniters, ignition coils, spark plugs and other components were replaced for comparative inspection. The phenomenon of carburetor backjet could not be eliminated, which indicated that the phenomenon of carburetor backjet had 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, Instead, the ignition advance Angle "F" mark on the magneto rotor is aligned with the engine block timing mark. The inspection results show that the opening time of the intake valve is advanced, and the valve phase of the engine is 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 incorrect, usually,

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

Second, the timing driven sprocket connecting plate on the camshaft is misplaced with the camshaft.

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, the results of the inspection to 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, Instead, the "O" timing on the camshaft timing driven drive sprocket marks the timing on the cylinder head of the advance engine. The inspection results show that the reason for the early opening of the intake valve is that the engine's air distribution timing is incorrect.

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 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 can align to the engine block timing mark, The check results show that the valve phase of the engine is correct.

Start the engine for acceleration inspection, the engine acceleration performance is obviously better, the carburetor is still more or less a little back jet.

The carburetor oil - water level is too high, can also cause the carburetor slight backjet phenomenon. Remove the carburetor from the engine, increase the working height of the oil float, and reduce the oil water level of the carburetor.

After installing the complex carburetor, start the engine for acceleration inspection, the engine acceleration is good, the muffler issued by the "spit, spit" exhaust sound disappeared, there is no black smoke emissions. Drive a motorcycle to carry out road test and test, and the motorcycle runs normally at high speed.