A friend gave me a non-running 4218 Craftsman that Poulan made about 18 years ago. It had a broken pull cord from a frustrated owner who gave up on it. He said, "Edwin, you can keep this thing. It's junk."
Amazingly, the only thing wrong was the spark plug was loose. I started it on the third pull after fixing the pull cord, cleaning the plug, and tightening it down. I used it for awhile and never had any trouble. Good little limbing saw. I should sell it, but for some strange reason, it's still on board and resting in its storage case.
I'm certainly not an expert, but I have learned a lot about these saws through the years. There was one straight-gassed Poulan Pro that I tried to save by rebuilding the top end. While bolting the new cylinder tight to the case, it cracked right down the side. It was a sickening sound. The local Stihl dealer said I was nuts to even try to save it.