Holley 4779 750 cfm Double Pumper
Demon,
I have the same book. You missed the word 'system'. Idle system. Because the idle jet is part of a system that controls idle AND off idle.
Some emission carbs had limiter caps on the idle mixture screws to stop tampering & rtetain the lean idle for emissions. Do you think the caps were added so that folks could lean the carbs even further? Of course not. Limiter caps were used to stop folks richening the idle because there is enough idle fuel at idle to richen the idle.
If you read Ruggles book, his 'recipes' of engines with different cams etc, at the same time that he talks about enlarging the idle jet, he also enlarges the Idle Down Channel. The IDC [ T-slot restriction on Holleys, Economiser on Carter/Edel ] supplies the transition slot for off idle fuel. It is for the IDC that the idle jet is enlarged, NOT for more idle fuel.