1. The carburetor has poor atomization effect. Whether it is the plunger carburetor or the vacuum film carburetor, its temperature adaptability to the external environment is relatively poor. Then pouring boiling water on the head of the cylinder improves the atomization effect of the carburetor to some extent, so the vehicle will be easier to start.

2. Insufficient negative pressure in the cylinder, the insufficient negative pressure in the cylinder of the motorcycle, the temperature inside the engine will rise slowly, while pouring boiling water on the cylinder head will quickly promote the temperature inside the engine cylinder, which can make up for the starting difficulty caused by insufficient negative pressure in the cylinder to a certain extent.

3. Poor flow performance of lubricating oil, the flow performance of lubricating oil in the state of cooling machine will be relatively poor, if you pour boiling water on the cylinder head to a certain extent, it will improve the flow of lubricating oil, so that the running resistance of the engine will be reduced, so the engine will be easy to start some.

Clear out the main cause of this phenomenon, we can from these three aspects to this fault ruled out, first of all should change liquidity better lubricating oil to increase the speed of the engine, to improve carburetor atomization effect, it is necessary to readjust the fluid level, in the actual repair slightly dispatch fluid level higher, carburetor atomization effect will be improved, the engine starting performance will be improved.

Secondly, can also be ruled out the fault by enhancing the engine compression, should first check valve clearance, if the valve clearance is normal, when necessary to disassemble the machine maintenance and repair, usually a piston ring wear, will be the lack of engine compression valve leakage, so after grinding and replacement parts to corresponding the fault disappear.

But if the engine starting performance is not very poor, power is no obvious decline is not necessary to completely disassemble machine maintenance, can do the heat preservation measures suitable for motorcycles, such vehicles would be much easier when start again, but don't often on cylinder head pouring boiling water, this will only make the engine relies on this kind of means to make it start performance worse and worse.