With any ringed engine, you'd normally run it extrememly-rich at full throttle for the first 15 minutes or so...about 12-16 ounces for the SuperTigre .90. You would gradually lean it a bit at a time over the next 32-48 ounces of running. After about 48 ounces of fuel have run through the engine, it should be able to be leaned near peak RPM. The "pinch test" is one way to help you determine if the engine's needle can be leaned. If the RPM increases when you pinch the ine, then the engine has "room" to be leaned.

The method mentioned in the SuperTigre instructions has been proven over decades of use. It works very, very well.