You need to figure out what circuit is in play in the area of operation you want to make leaner. At 25% throttle opening you may be on the transition slot(idle circuit) and not the mains.
The transition slot gets fuel from the main well through a calibrated orifice called the idle feed restrictor (ifr). The ifr also feeds the idle discharge holes which are metered by the mixture screws. The t-slot and the idle discharge flow until the velocity of air through the main well is such that the pressure in the main well becomes lower than the vacuum present at the t-slot. Once this occurs (and contrary to popular belief) the t-slot begins to flow backward introducing air into the main well effectively acting as a main air bleed and is how the idle circuit calibration can influence main circuit calibration.
Edit: The above applies to a Holley style carb which is what I assumed the OP was working with.
1973 Mustang Convertible
460 D0VE-C Heads w/CJ size valves, Lunati voodoo 227/233 cam, Edelbrock performer rpm manifold, FPA headers, Holley 950 HP carb, C6 w/2500 stall converter, 3.25 trac lock
Last edited by TommyK; 02-16-2017 at 12:03 PM.