i recently bought this bike it had been sitting for a year, and took it on its first run about 200 miles.it did very well.every now and then during tripit would act like it was loading up and popping slightly,went on another shorter ride and it did a little worse then this week went on a short run and it did horrible.exhaust popping lack power on high end. changed plugs and cleaned carbs does this sound like a timing issue and if it is where do i start? any imput is appreciated