When I got my Savage 25 RTR, the guys at my LHS told me to get a hump pack (which I did) and that I should take off the throttle return spring. They said it can not open the throttle fully with it on and it gives you faster throttle response with it off. Made sense to me so that was the first thing I took off. After break in and with more then a gallon thew the engine, it started to come alive. It would wheelie sometimes but just on grass. There is a pretty small, tight race track near me so I replaced the stock spur with a 52T. Since then it wheelies all the time. Even on pavement. And that was with the stock air filter. It was a short time after that I did the Diff mod (front and rear), put in reverse, and got a Motor Saver air filter (I can't honestly say that I seen a big difference from the stock filter). I never changed my rear shock oil, I'm I am currently running a 2 speed tranny (my three speed is in the mail!), my exhaust is stock, my engine is stock, my clutch is stock. I'm into my 5th gallon of fuel (20% Powermaster since day one. You may have seen the advertised links on this forum.
http://www.powermasterfuels.com/ ) and it still wheelies on pavement.
I guess I did something right.