You say it back fired a few times? Sounds like maybe you are 180degrees off on your cam. turn the gas off, unplug spark plug and ground it.....Have someone kick it over a bunch of times while putting your hand over the end of your exhaust. (gloved). is it blowing air out or is it sucking it in? Like wise you can see if you are blowing air out the carb instead of sucking in. Humor me?