Lean condition under light acceleration
As the load increases, vacuum drops, and the transfers should be supplying more fuel.
A/J I think you know better 'cause you do know this stuff.
Assuming the carb is pulling from the 'idle circuit', as vacuum drops, there's going to be less fuel moved from the bowl to the slots.
Also, assuming the carb is on the idle circuit, the power piston isn't going to matter much if at all. The restrictions that will matter will be the IFR etc.
I think, based on what's been posted, that these tests may be when the carb mostly onto the main circuits.
The question then is whether the rod jet combo is too lean, or whether with this engine the power piston needs to lift the rods at a higher vacuum.
Generally the more radical the engine, the sooner it will need to be supplied with enrichment. But it depends on efficiencies and fuel distribution so this is just very general.
If this is happening with manifold vacuum well above 11"Hg, then more likely that the rod jet combo needs to be richer.
If its around 11 or lower, then would try changing the springs so it steps it up sooner.
