Have you read over the section on carb adjustment in the manual I posted, particularly pages 15-16. This is the procedure which I follow. The idle mixture and high speed mixture screws will not change your RPM's very much. Their job is to control the amount of fuel for various speeds. Your idle speed screw controls RPM's at slow speed and a properly set governor. This is covered in the section entitled "Governors and Linkages) in the manual. This explains everything much better than I can. Tachometers for small engines are out their and rather expensive. Best bet if you really want to get one would be to look for one on line. I use one called a VibraTach, but don't recommend it unless you can find one to instruct you how to use it. Electronic one are $$$$ and unless you are in the business not a wise investment. TinyTacs work also.
