If you look inside your GTS air filter, you will see that the air passes through the filter, then negotiates its way through a U-shaped aperture in a central diaphragm, and finally works its way into the end of the induction pipe, which extends quite far into the filter box. Not very conducive to good breathing!
Being the inveterate fiddler that I am, I atacked the aperture in the diaphragm, opening the curved part of the U by 1/4 inch, then cutting away the corners to make a round-bottomed V shape, more-or-less doubling the size of the aperture.
I did not touch the induction pipe, as the length of this pipe is critical for tuning the engine's torque curve. But it is tempting to remove 1/2". In 15", how much difference can 1/2" make?
Anyway, the result of my fiddling is better acceleration right across the speed range, and my scooter now holds 105-110kph up a nearby steep hill where it was dropping to 95kph!
On the downside, the scooter is a bit more noisy at low speeds - up to about 60kph. Beyond that I don't notice it, and if I had an aftermarket pipe I would not notice it at all. Anyway, a lot of members here like a bit of noise. But under hard acceleration from a low speed, it sounds a bit like a two-stroke, and twice I have tried to change gear when accelerating!
I have discussed this mod with Paul of PM Tuning, and he has offered to try it on the dyno if I send him pictures and measurements. It would be nice to have my seat-of-pants evaluatioon verified by him. watch this space ...
Last edited by Mike Holland on Sat Feb 20, 2010 5:39 pm; edited 1 time in total