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。 。
2
The results also showed that much more steady combustion could be obtained with mechanical spray nozzle than with steam atomizer for some burners with poor performance.