Alright Bro, First things first, Calm down. If I paniced everytime my sled backfired I would be insane. I have ran a sled on one cylinder for a long time, not a great thing, but, not fatal, especially if it was only for a minute. Like everyone already said, check compression first, you can do this the same time you check the plugs. Pull the plugs and put your finger over one of the holes (unless you have a compression tester), and turn the motor over. if it can push your finger up a bit, you have compression, do the same on the other side. Put new plugs in it. Once a plug soaks up fuel, no cleaning can save it, it is always better to use new plugs. Also, check to make sure no one has jacked with the idle on that carb, I rebuilt my motor last year, put it in and it was only running on one cylinder, I sweated for a second, then realized that someone has screwed the idle adjuster all the way out on that carb. Also, you probably have some crappy gas in it, if it is about empty, pour some new gas in it, if it has more than an 1/8 of a tank, suck the old stuff out.