Do a little reading on site (via the search engine) and you'll notice that very few have had a good experience removing the air box without other very substantial modifications. Our collective experiences will tell you that the GeeZer runs like shit without the air box. Muffler mods are just about as worthless (unless you just want louder).
If in fact you pick up 10% extra horsepower (which I kind of doubt) you'll go from 18 hp to about 20 hp. You are going to spend a lot of time and money to get
maybe 1.8 hp.
That's just our collective experiences. You may know better that us, but I think you'll find that a 16 tooth front sprocket and a needle shim is the easiest way to mod the GZ for
slightly better performance.
You can do what you want, but I doubt your experience will differ from ours. The GeeZer is what it is.
Good luck.
