im ok at tuning did it for yrs in karting, with the tilitsons,
i leaned and richened because i thought the same thing, didnt help, full to near empty on the tank doesnt matter either,

AL, my set up looks just like yours as far as the mounting with the hole behind the carb, the tube for the air hole in the plate maybe be just what i need, thats where i was thinking the problem lies. what did you use for a nipple? and did you tap it?