hey you live in boston too. we've got plenty of moped riders around here. it doesnt sound like its too big of an issue. brakes are easy, you might just have to get new brake shoes. i doubt the springs are worn ive never head of brake springs wearing. when you say you open all the way and it stalls or coughs do you mean it starts to make a low pitched growl? if so tahts called bogging.you are probably jetted too high or too low. if you didnt make any changes to this bike it may just need a filter cleaning, pipe cleaning, carb cleaning, or all of the above. if your filter or pipe is clogged your bike will not get enough air and too much gas. taht is bogging. or maybe your jet is clogged and you are getting too much air (running lean). the brakes may just need a cable adjustment or something.