>>What size larger of a jet do I need to use with the bi-turbo? Is it like one size up?<<
Usually one or two.
Best bet is to do some "Plug chops" as described in Freds Guide, and figure out where to go from there.
>>Is the biturbo pipe the best in terms of price and performance?<<
As a general rule, yes - tho some folks here have ordered other models and are quite pleased with them, so ask around and make sure.
>>If I want more top end speed, how many teeth should the sprocket have? How bad will this kill me on acceleration?<<
I dunno about Puch...for Tomos it's 27...basically more teeth on the front = more top end, less acceleration.
With the BiTurbo pipe, you tend to get an improvement all the way across, power and top end, which is why I reccommend both mods, what you lose to the sprocket in acceleration, the pipe will give you back.
So you don't really lose any acceleration, all-in-all.
Some folks say best one mod at a time, but I am of the opinion that the Pipe and Sprocket works better as a combo than individually.