Did you stuff the crankcase to decrease the crankcase volume or use original spacing from the inside of the backplate to the crank? I don't go any lower than.015" and to a max of .020" Also I know of an r/c boat engine modder and converter that cuts out for the port to give better flow.He does this by filling the area on the back of the backplate,where the cut would be with JB Weld and then cutting it out in the right area.I haven't tried this yet on an aluminum stamped or plastic backplate.I had a cast aluminum backplate on the engine above that had this done from where it was made.I don't know what it was made for ,but it fit the 30cc Homelite and gave me a space of about .018.Also adding an 11 mm venturi carb will wake it up .Ask my 21cc Weedeater Featherlite trimmer.Here's a pic of the backplate.