Hi there. This past evening, I picked up what I believe is an older Stihl trimmer. It is model FS 51 AVE. I did get it started, and running, but transition was very bad and slow. This is when I saw the tank was slightly cracked in both rear edges/corners. No big deal, I will take the trimmer home, and plastic weld the fuel tank back up. However, this led me to wanting to know what size engine this trimmer has on it, as well as an instruction manual for it for my own knowledge. This is a neat looking little trimmer and does run decently. Looking forward to many hours of fun with it! Thank you.