I have a 2000 sportsman 500, it has been a very reliable machine. Taking it in the road, it seems underpowered and although I have the thumb throttle is fully pressed.i won’t reach full power and seems very noisy around the air intake box, I have had it serviced to try and cure the problem, new spark plug, ht lead,new air filter, carb cleaned and serviced, any help would be appreciated,