How about this....

The Mixture Control Valve (Mixture ControlScrew):
For asjusting the mixture strength at part-throttle and idling speeds, to obtain steady idling and smooth acceleration to medium speeds. The mixture Control Valve has been factory set for the approximate best result. First, run the engine as received, and re-asjust the Mixture Control Valve only when necessary.

do you fly planes?
what do you fly?