I have a 2003 john deere gt235 with a B&S engine. when the mower deck is disengaged the engine surges up and down regardless of where throttle is set. a previous mower I owned would do this if the air cleaner was extremely dirty. that is not the case this time.
Remove the carb and give it a good bath and cleaning. When you put it back together, I would install a new float needle and seat. I'm thinking it is probably part number 398188, but take your engine numbers along to the repair shop and have them double check. If you have trouble installing the seat, post back and I will give you a step by step procedure to do so properly.
