Believe it or not, you are fully capable of adjusting the carburettor on your Ryobi grass trimmer yourself. You do not need the help of a small engine mechanic to get your Ryobi trimmer running smoothly again. If you can start the engine, you can make the necessary adjustment. The engine has to run in order for the adjustment to be made accurately.
Start the engine and hold the throttle so the engine will warm up quickly.
Allow the engine to idle. The idle adjustment screw is located on the carburettor. Turn the idle speed adjustment screw clockwise with a screwdriver to increase the idle speed. If the engine idles poorly, increasing the idle speed will smooth the idle out.
Increase the throttle, allow the engine to run at high speed, and release the throttle so the engine returns to idle speed. When the idle speed remains even, the idle speed adjustment is complete.