My Ryobi 30020B string trimmer will only run if I keep the throttle almost fully open, otherwise it dies. So far I have done the following with no fix:

Checked and clean spark plug, removed and cleaned exhaust and spark arrestor, new fuel with 1:50 oil mix, cleaned fuel filter, cleaned air filter, opened and examined inside motor and it looked clean and shiny and fine, adjusted throttle screw to higher setting, removed, disassembled and cleaned carb with carb cleaner and air compressor through all holes. This is a diaphram type carb so not much too adjust. It is a Walbro (WYC) and the only numbers on it are 4 526. Gaskets seemed in good condition.

Any ideas? My gut tells me it is the Carb but I can't actually find the problem. Help please! Thanks a lot

You should have replaced the diaphram in the carb,this most likely the promblem.