Craftsman 18 HP-OHV Model # 917-274822 will NOT run at Full speed only idle

Hello I have a Craftsman 18 HP-OHV Model # 917-274822 will NOT run at Full speed (will start) but when I give it gas the engine will not run any faster, the throttle cable is working I can see it moving on the carburetor, this is what happen it was running fine while I was cutting grass, and in the middle while cutting grass the engine started to run at HALF SPEED.

I have replaced the sparkle plug, fuel filter, i took out the air filter and check the gas, still it will NOT run but at half speed (engine wise) any suggestion???