ok....here we go again.
i'll try to keep it short
how it works:
the resonator (original name for boost bottle) absorbs the return pulses that sneek across the reeds. the pulse causes a double-enrichment effect. absorbing the pulse makes the air pass one way at low throttle positions.
what it's for:
the point of eliminating the double enrichment is for better metering at partial throttle. for this reason, you do actually have to richen the pilot vs. the x-over pipe. on larger 2 stroke engines, such as snowmobile engines, there is much more noticeable effect on both top and bottom because the resonator works as a crossover passage where there was not one before.
what it actually does:
on the banshee- mutes the snap, giving a more gradual power increase. the only 2 uses i found for that effect are, better controll on verry technical trails, where throttle controll becomes difficult, and giving my daughter a ride around the yard, up and down hills. other than that, it just takes the fun out of playing around.
on a snow machine- if you want to keep from burning up belts trail ridding, it's a quick bolt-on solution with a slight added boost effect in the midrange, coining the nick-name "boost bottle"
facts:
Yamaha developed the resonator
Yamaha uses the crossover tube on the banshee because it performs way better.
the resonator was designed for 4stroke, and not as a shared chamber.
hope this helps for now. i will have dyno tests this summer running bottle, tube, and plugs on different reeds, timing, and filter setups on a low-mid bike