You need to establish a true performance baseline, as most speedometers are off by around 20% when tested vs a GPS. You should also use an accurate tachometer as they are also inaccurate.
Exhaust: stock tested shows no restrictions, but some "performance" do make more noise so there is some safety issues. also the better ones are designed to allow easier removal of the rear tire for service.
Variators: Tuning both the engine & clutch will yield better takeoff, decel and higher rpm top end
Carburetor: check the plug,if it is clean and tan color, then the fuel is about right; increasing fuel may not get any more performance on a stock engine. Fine tuning the carb with a 4 or 5 gas analyzer is best, but most can't afford one
CDIs & Performance coils: I have not found the need for them and in fact many of the BBKs I buy have them included but I don't use them. Currently, I have some for sale on CL. in case anyone is interested, here is the link
http://atlanta.craigslist.org/eat/mpo/5382456731.html