帮忙翻译一下呗

Take the truck off the ground, and open the throttle fully. The engine should run cleanly until it reaches 80% of top RPM, after which it should start to run slightly rich (4-stroking):
• If the engine runs cleanly all the way up to top RPM, richen the main needle (counter-clockwise) until it starts to 4-stroke at approximately 80% of its top RPM
• If the engine runs too rich (4-stroking all the way) lean the main needle (clockwise) until it only starts to 4-stroke at approximately 80% of its top RPM
说明书上调节引擎中的一段，请教一下其中的4-stroking是什么意思？
还有，按他说的这种调油针方法是什么道理呢？谢谢

应该是类似四冲程引擎的声音。 你去找2台摩托车听听比较下。

将车离地，及把气阀全开。让引擎清油至达到80%的最高转速，之后比启动时应该有些微地富油,要是引擎运行清油后能达至最高转速，把高速油针调大(反时针方向) ，只有启动时的(4冲程声音)至大约80%最高转速。要是引擎运行过于富油,将高速油针(顺时针方向)调小至只有启动时的(4冲程声音)至大约80%最高转速。

以上是從置頂的【化油器的調較】中節錄下來的，相信是同一來源。