imo..on ebay id look for an 88cc big bore not caring what brand id pick up a cheap one for mmmm probably around $100 and for kicks and giggles and to make it sound beast a cheap inner rotor off of ebay for $30..you willl notice increase ...what amount you looking to spend?
yea as i dont see much of a exhaust right now. A bigger carb wont make much of a difference as youd like so stick with what you have unless you were going with a bbk. After spending everything you just noted youd prolly spend less on a BBK and will get a much more noticeable difference.
get a BBK for a e22 head you should be able to get the Tbparts 88 kit for a 100 bucks and that piston will work with your head as im almost positive its a e 22 or one thats just like it and youll get your best bang for your buck.