Most Ryobi carburetors can be adjusted with a flat-head screwdriver if the problem involves frequent misfires, engine stuttering, racing or stalls. These problems usually derive from the engine's air/fuel mixture and can be solved by adjusting the idle or using a higher-quality fuel.
Ryobi engines, whether of the two-cycle or four-cycle variety, are simple motors built for lawn and garden trimmers and blowers. When a problem arises, it is almost always due to the lack of air, fuel or spark.
The carburetor can be adjusted for idle speed by turning a flat-head screwdriver bolt on the carburetor counterclockwise for higher idle or clockwise for lower idle. If the engine is racing too fast at idle, turn the bolt clockwise; if the engine is sputtering or stalling while running, adjust the idle bolt counterclockwise until a smooth idle is attained.
If none of these steps solve the problem, replace the engine's air filter and flush and refill the gas tank, making sure to use the mix of gasoline and oil specified for the machine. Check the wires to the spark plug, then remove the spark plug from the engine, ground the plug and attempt to start the engine, observing the spark plug for a spark near its insulator.
If none of these solutions work, consider taking apart the carburetor for a thorough cleaning or buying a new machine. A warranty may cover the replacement.