Is that opposed to low ethanol fuel or no ethanol fuel? We had tuned the idle mixture all around and the jets are the standard for the Holley carb. The plugs have been almost scary clean, so nothing indicates being on the rich side. But what you say on the lean with high ethanol makes sense.
The firing "unevenness" that this helped is pretty subtle, and sounds like if a 1-2 hydraulic lifters were a bit 'lazy' , or 1-2 soilds were misadjusted by maybe .005" .
