do not tune ys engines for max rpms they like to run rich and leave smoke trails. the 20 20 fuel breaks down fast with high heat since it is synthetic. it is not like castor which can be run at higher temperature. The high and low speed are set like a conventional engine but the engine has to be under 200o rpm to set low speed. you let it idle for 20 seconds after first revving it high to clean it out. the pressure regulator is for fine adjustment to the mid range after high and low are set. for setting high and low a good starting place for pressure regulator is flush. after high and low set then you clear the engine at high rev and then reduce rev too about 3000 for 20 seconds and observe response when you rev it up. if it is loaded up turn the regulator in if it cough or dies instantly turn the screw out.