so while im riding my x7 2 stroke 49cc it will like sputter or make a stalling feeling while riding then it will continue to pick up speed but if i slow down again and try to pick up speed it will do it again and pick up speed once again. i checked the part where the exhaust was screwed in and nothing is lose there. also the bike has been sitting for a month now and it was not doing this before. oh yeah and changed the spark plug also since i thought that could have been the problem