1994 Bayou 400 shift problems.
 

I just bought a 94 Bayou KLF400 4x4, and since I got it home, have been having some shift problems.
It started off by the machine not staying in 4th. It had been sitting a while, so I changed the oil, but DID NOT use a wet clutch oil, I used normal 5w-30.
I tried running the machine and it would not stay in any gear above 2nd. When I tried to shift up to 3rd, it would keep making a popping sound and lurge forward and when I would try to shift it up another gear, the machine would almost lock up to a stop. I played with both clutch adjustment screws (I hope I did not mess anything up with the lower screw..advise?) and not much help.
Even in SL, and in first, it almost sounds like it is only 3/4 of the way in gear. Some ratchet sounds.
Where do I begin? Clutch or tranny? Does using the wrong oil and clutch adjusments cause this kind of shifting problem, or should I tear the beast open?
I searched but did not find anything too similar except for a post about adding 4mm of weld to a spring perch on the shift shaft? Huh?
How far must the engine come apart to access tranny parts? Can you just remove both sides to replace parts, or do you have to gut the entire block, piston and all?
Any help would be appreciated as I really want to play above 10 mph.
Thanks.