A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle.

二冲程发动机没有移动的阀，火花塞每次点火活塞到达循环顶端。

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Poor fuel quality. Incomplete combustion and lack of sealing between piston and cylinder wall or badly losing valves. Possibly incorrect engine timing / set up.

燃油品质差，不完全燃烧和活塞与气缸壁之间的密封性差。 。

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