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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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.

对于稳燃效果较差的燃烧器，采用机械雾化喷嘴可获得比汽力雾化喷嘴更为稳定可靠的稳燃性能。

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The EPA pulled off the feat by sharply increasing the amount of oxygen-poor exhaust that is recirculated into the combustion chamber and increasing the pressure of the fuel being forced into the cylinder.

FORBES: EPA, Inc.