I would like to add a comment about Evolution/MVVS gas engine timing. I have been able to change the timing on every engine for the last three years. My last engine would not let me change the timing. After many attempts, I contacted Horizon support about my timing problem. They called me back a day later and told me that you could no longer change the timing and it was not needed any more. They could not or would not answer why the directions still show how to change the timing and why do they still provide the shorting tool and the engine still comes with two magnets for the pick up.. The engine runs so good the way it is, I decided to drop the whole matter. If I ever changed to a tuned pipe, I guess I would be out of luck.