Got a 2005 400 sportsman that is not responding well to the throttle. Runs fine at slow speeds but when I juice it, 50% of the time the atv will sputter and hesitate before accelerating. Usually have to back off and accelerate slowly. The machine only has 60 hours on it and I had the shop do a break-in service at 10-20 hours a year ago. I just changed the oil and installed a K&N air filter. Still seems like it isn't getting gas. Any ideas? I have put Sea Foam in it in the past but that is usually it. I run it all year round but not much as the hours indicate.