new carb setup ??

[robb]

i have a 1981 250r, with boyesen reeds and a reed spacer, with a stock 1985 carb(34mm). and no airbox and with a uni filter . i cant seem to adjust the carb properly it boggs out in 3rd high revs, so i played around with the screw now it does the same thing in second?
do i need differnt parts for the carb like new jets, or is there a starting point for the air screw????
any ideas would help thanks