In addition to the highest idle vacuum (always a good starting point), the critical jetting to compensate for high air temperature (and/or high elevation) is done on the main circuit's high-vacuum event. Depending on the type of carburetor, this is controlled by:
1. the main jet size, or
2. a combination of jet size and metering rod diameter (AFB, ThermoQuad, QJ, Edelbrock), or.
3. a combination of main jet size plus power valve channel restriction size (Holley 4150)
The typical R&D is reduce main jet size by 1 number and test cautiously to see if cruising vacuum is increased. If yes, test for knock at full throttle.
