BTW, you can also just grind away the cast key all together. Mark with a pen on the outside of the flywheel its position and using this mark and the key-way in the crankshaft, Line up your timing or advance it slightly for more power at rpm's or retard it for a smoother idle. Now a "slight" adjustment is only about the width of the key-way or less. To much advance and the motor will "pop" at high rpms. I've tweeked on my ryobi this way and went too far till I heard it pop and moved it back a frog's hair and it quit, got 600 rpm more from the motor but what a rough idle. If your flying a Cub with it, go with a bit larger carb, free breathing muffler, large dia./flat pitch prop and pull the timing back for a smooooth running motor with good torque. A fire breathing motor isnt always the best way to go if your just wanting to shoot touch and go's late in the afternoon from your lawn chair with your favorite floater. I have a number of ryobi 31cc's and homie 25cc' and 30cc's and there all setup differently in regards to timing and carbs. Piper