If it's too lean in this area, the bike will feel really flat and down on power, but will respond quickly to changes in throttle position. Too rich jetting (too much cutaway, needle positions too high, too large a needle jet) can make your bike lunge and hard to control.
Due to the hassle of making changes to these circuits, these are the most neglected areas of tuning.
Your slide cutaway (or throttle valve) needle and needle jet will all affect your bike's acceleration from one-quarter to three-quarters throttle, and this is the most important area for off-road riders, since we spend the most time at these throttle settings. Even though they may differ wildly in size, shape and design, all four-stroke carburetors have the same basic parts or circuits. Your engine is basically an air pump, and your carb meters how much air and fuel are sucked into that pump.
