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 Sun, 21 Feb 2010 01:39:46 +0000; edited 1 time