hey andrew, the screw on the carb adjusts idle speed, there is no idle mixture screw or jet, just the main jet and a little idle passage in the carb body at the bottom of the slide is the idle 'jet'. 47 is probably the stock jet, if the carb is be a 12.10, should be ok for the summer but you could go richer. do some plug chops to find out if you are running rich or lean, read about plug chops and how to read plugs in the wiki, also go through fred's repair guide.
you did not mention the exhaust, how is the flow? it could be built up with carbon, you can burn out the pipe and clean out the exhaust port on the jug
is the variating transmission under the left cover working correctly as the engine spins up?