heres how they work...
http://imageshack.com/a/img140/7093/valvef.jpg

I just made my own for my XR250 a couple years ago...
never got the sprining right... but were still beter than
damping rods...
http://imageshack.com/a/img233/8521/ssa41922.jpg

http://imageshack.com/a/img32/7183/ssa41921.jpg

__________________
Harley Davidson..
The easyest way to turn gasoline into noise with out the side efect of horse power...