Well, the carb I have is a RS151B648. No idea what the 648 means but since they made A's and B's, I'm gonna guess it is a later carb. Anyway, with the governor valve blocked off it adjusts like the sheet you sent above. That is, I set the idle "normally" like in the memo, then open the throttle and try to find where the high speed needle leans out. It will not lean out and it sputters under load, richer than it should be. It isn't horrible since I blocked the governor (it got better when I did that) but it does not run right and it is hard to convince myself that it could not run better if it was leaner.
I have not taken the carb apart to look for the fixed main jet but I gotta believe its just like the photo above. I am suspecting there is a defect somewhere that is letting fuel past the metering system. Maybe the high needle seat is damaged and won't seal when shut or possibly a porosity in the carb body letting fuel bypass. ???