I called Poulan today regarding my Poulan Pro PP4218AVX and the tool less chain tensioner. It never stays tight and tosses chains often. There are many comments on many websites referring to problems people are having with this system. I asked them about it and they said they can send me a kit that does away with the tool less tensioner and makes it a tool required tensioner.... that is, I can tighten it with a wrench.
The kit has a cover and some nuts. They are shipping it to me. I asked how much it will cost? Nothing. It is under warranty.
Should be here in a week. Will report back once it arrives.