I just bought a used 1998 Polaris Ultra SPX 680 cc, 3-cyl., 3-carb. While initially accelerating to a specific speed the machine performs like expected. However, when I reach a desired speed (anything over 30 mph) and try to accelerate the sled will not go faster. It will hold the same speed even if I crack the throttle wide open. If I take the sled from a stop and hit it, the machine will go 0-95 like it’s supposed to. Only when I let off the throttle once I’ve reached my desired speed for the time it will refuse to go faster. So for example I accelerate on the trail to 45 mph and find a straight away and wish to go faster the sled will not go, I must stop (or slow below 30) and re-accelerate. Any idea what the problem is? The carbs are as clean as the day the came out of the factory. That was my only thought. Please help!!