Unless you're a very experianced tuner leave the third needle (or seat) alone. If you get that one messed up you may never get your engine running properly again without professional help. If it's off it may not run, may run badly, or may run hot just like if the other needles are off. The third needle is not really a needle at all, but the seat where the low speed needle goes into. Any adjustment to the "third needle" needs to be done to the low speed as well. If you turn the third in an hour, you need to turn the low speed out an hour also.