I just worked on a Ryobi for a friend. It seemd low on compression at first and could not hand start it. After some running and tunning the compression got better and it will hand start now also...but you have to have it tunned real good for hand starting. It had a kinda a unstable sound at full throttle. I put new tygon fuel line in complete install. I noticed little air bubbles in line after purge bulb. I removed that purge bulb completly and air bubbles dissapered and engine finally run even at full throttle. I do think the stock muffler should be gutted some for more RPM. It sure idles good and reves up very good and quick. Funny thing...not much vibes at idle and fairy smooth a top RPM, but has a nasty vibe about 1/4 wide open. Is this normal for a 31cc Ryobi? Thanks Capt,n[X(]