carburator adjustment?

i have a ryobi ss30 start plus model ry30040a. it starts and runs. it boggs down from 1/2 to full throttle. i cleaned tthe carb. blew out the fuel lines. if i hold my thumb over the carb intake it will shut off. if i partially block it it will rev up and run good. i dont see any carb adjustment screws anywhere. the only thing i can see is maybe bending the arm that opens the fuel supply below the diaphram. is there a hight adjustment procedure for this. is there any adjustments??

Jared Thompson
July 2011