Use a tach to get the most from your 4 Stroke. Also, break in your engine per manual and it will last longer and run cooler. Adjust the low end with the fuel line pinch. At idle, pinch the fuel line to the carb. The engine should have a slight increase in RPM just before it cuts out. If the RPM's do not increase before it cuts off, it is too lean. You do not need a tach for the low end. A Horizon Hobby rep showed me how to use the tach to tune my Saito 125. After the engine has ran several tank fulls and is warmed up, run engine to full throttle. Use tach to get highest RPM by adjusting the high end. Once you reach the max RPM, richen the high end just a little to drop RPM's about 250-300. This ensures you are getting the max RPM's while not leaning out the engine when in flight. I have done this to my Saito 82, 100, and 125 and they all run great with wonderful flight times.