Help, I'm New

Looking for help. I have just bought two 1996 Polaris SL780 and SLX780 and am having alittle problem. The sl780 run fine abit slower out of the hole than the SLX but I think that to be normal. My main problem is with the SLX, I do get sputtering at all the different rpm ranges, or it seems to happen when I turn sharp corners. Another problem is at full out high speed it will just shut itself right of(this will also happen few timeswhenh spinning 360's.... Also could anyone tell me where to get decent parts for these machines as well.

Any help would be greatly appreciated...........