A nearly constant air-fuel ratio is maintained by the main metering system from part-to-wide-open throttle. 从节气门部分开启到全部开启，主计量系统保证了空燃混合比几乎恒定。
For firing of the mixture in the cylinder every time spark occurs, the air-fuel ratio must lie in a fairly narrow range. 为了在气缸里每一时刻发生一次火花时混合气的燃烧更理想，空一燃混合比必须限于相当狭窄的区域内。
