"Book" settings on any model carburetor are only starting points. You will have to adjust the carburetor to get the proper performance. The high-speed needle should be leaned so that the engine is rich of peak RPM at full throttle and doesn't overheat. The low-speed needle should be adjusted to give a good idle consistent with tood acceleration and midrange. Many people try to idle their engines too slowly, which causes difficulty with acceleration and midrange.