Small Engines (Lawn Mowers, etc.): Ryobi riding mower, throttle plate, speed circuit

Question
Ryobi riding mower, 17.5 HP B&S engine 42" cut.

When I engage the blades the mower loses alot of power. It still mows, just real slow. Then when I disengage the blades it seems the motor runs faster than normal and the speed picks up. This just started today.

Answer
Have you checked the air filter?  It is possible the carburetor high speed circuit is dirty.  When you load the engine the governor opens the throttle plate wider which uses a different carburetor circuit.

Have you ever cleaned the carburetor?  How old is the mower?

Eric