I was given a craftsman 18" chainsaw for christmas by my parents. I've used it for about 30 minutes before today and everything was going fine. 15 minutes in the chain pops off so i shut it off and re-tighten it. Start it back up, and then about 10 seconds later is stalls out. I checked the gas and noticed it was kind of low so I put more in. Start it back up and then about 5 seconds later it stalls out again. I repeated this proces about 5 more times, gave it 20 mins to cool down and then started it back up. It ran for about a minute before it stalled out yet again. What do you think could be the problem?