I have a 17hp 42" craftsman lawnmower, which is about 6 years old.
After I mowed and the mower cooled down, I started the engine, but the speed kept pulsating up and down without moving the throttle (despite the position of the throttle). Now the mower pulsates and backfires when I first start it. When I checked, the little arm (governor) moves back and forth as the engine speed changes. I thought the fuel might be a problem, so I went to Sears and got a new fuel filter (the new filter is bigger and has a clear display for viewing the fuel and filter element). Once the filter was installed and the fuel tank valve was opened, it only filled the filter half way. I restarted the mower, but it continued to pulsate, so I checked the filter again and the filter still was not full of gas – is this normal?

Hi,
Yes, filters only filling partially is quite normal. Suspect trash in carb or notched flywheel key. I know they are very different, but the latter happens from repeatedly shuting off the engine at full speed.
Peace,
Clarke