I have a 1999 Simplicity Broadmoor Lawn Tractor with a B&S 14HP Vanguard Twin V engine. I bought this at a Simplicity dealer about 4 years ago and it was in excellent shape and has never given me any problems until now. The other day I was cutting as normal and decided to take a break. After about 1/2 hour I got back on and started it up. Immediately I noticed it was running at a lower RPM. It seemed too slow to cut grass properly and would almost die out when I went across some thicker grass.

I have checked the linkage on the carb and governor and cleaned them and replaced the fuel line from filter (new about a month ago) to fuel pump and pump to carb. I still have enough to replace the line from tank to filter, but right now may not have time.
One thing I noticed was a the lowest "run Speed" I see the governor moving up and down and the engine kind of goes slightly up and down in speed. At "Fast" setting the engine runs and sounds fine, except it is way too slow.
Other than me replacing the fuel lines and cleaning the carb, is there another possible cause...Fuel Pump, Spark Plugs or something worse???