Look how it almost doesn't change throughout the range. That's a vacuum leak somewhere. There are "builders" here and "mechanics"...
both put stuff together, one is more an order of nuts n bolts..while the other is more calculated.... after those two get done blaming eachother why it has a bug/glitch...in comes the diagnostic tech.
I'm qualified and experienced in all 3. The operator isn't being very helpful with his statement, or he himself doesn't really get it...which would be a scary scenario. With a dual plane there has been known a tendency for the 2 center cylinders to be leaner, not the ends. Each bank of a dual plane feeds 2 cylinders on each side, 4 total for each side of the plenum....like 2,8,3,5 one side...then 1,7,4,6 of the other. There is no way for one side of the carb to accomplish leaning out all 4 cyl on one side '2,4,6,8' because 2,8 are fed from the other side of the carb/plenum along with 3 & 5...while the others off the other side.
Imo Its leaking , be it some base plate leak or at the intake flange...or the bung the o2 is plugged into. One side is getting air after the carb...because it doesnt change af, not even half a point. Take it or leave it.
