sounds familiar.......... after replacing all electrical components.....coil to magneto we noticed oil leaking from the crank seal. was told by 3 sled heds near my place that this was my problem......i listened to many others say magneto , needles, seats, jets,
look for oil seapage under your recoil, there is a hole there, if the seal is leaking, it should be dripping to the belly. unless its on your pto side, the i guess you would need to pull the clutch.
do like what the last guy said too, take a look at your pistons, do a compression test when its cold , then when its warm and running bad.
or save yourself the trouble and take it to a dealer and pay him the diagnose time and fix it yourself.
......expect the worst....then it dont hurt so bad! lol