If you own newer toro 2x's read on: I had problems with the way my new mowers ran this season and mostly thought it was the fuel . The owner of the shop I deal with found out that to lean out the mowers and pass emmision standards toro changed the jets in the carb . These jets are the ones designed for high altitude( 6000'). Good for the guys in Denver but not me at 1000'. These jets are removable and can be replaced with jets that are available and were used in older carbs. If you live where you must have emmission tests you probably must leave it be. I don't and am changing the jets. This was done to mine and was told they run like the used to in the good ol' days.