Not running right

I ran my new-to-me 99 SnoPro this weekend and have a couple of questions. It's not running like it should.
First it kind of hesitates off the line and then it feels like it shifts gears and rockets up to 6500-7000 RPM , but then starts stuttering and will only run at 7000 (about half the time, it does better with new plugs untill you stop and start again)and eventually it will open up and rocket up to 8000. It probably hesitates at 7000 from anywhere from a second (only a couple times) anywhere to maybe 30 seconds. Mostly happened from a stopped start, would do better from a rolling start. Also starts cutting out at full throtle after a while, slmost feels like a plugged fuel filter or something.
Also it's running lean. Changed out the plugs a couple times to make sure.
Now here's my guesses (and I'm no mechanic. This is my first sled in several years)  The hesitation off the line then the shift I'm guessing it might have a dual or Tri helix in it, because the guy said it had a clutch kit in it.
The 7000 RPM thing I'm guessing is the power valves are in need of some cleaning and maybe even the update. I'm not sure if the update's been done to it.  
Also I switched oil from whatever he was running)I forgot to ask) It was red and had a sweet smell,  to Amsoil Synthetic green oil.
I need to know how to turn up the oil so it's not running so lean. Hopefully I didn't hurt the motor any. My friend said I probably didn't. We ran about 80 miles.
Other than all that, it was a great ride!
I would appreciate any of your input. If you could help, I'd greatly appreciate it.
Thanks in advance.