Small Engines (Lawn Mowers, etc.): Toro Lawn Mower, self propelled lawn mower, key way

Question
Why does my self propelled lawn mower idle rough, but when I engage the blade it run smoothly?  This happened after I accidentally hit a protruding stump with the blade running.

Answer
Tom
You may have put the engine out of time when you hit the stump. Take off the fan cover so you can see the flywheel make sure the key way is inline with the shaft.What happens when you are idling the idle circuit can not supply enough fuel to the carburetor, & when you put a load on it the high speed kicks in  so it will run smoothly.You may have to clean the carburetor.