I have one of those small chinese scooters with a 6.5 hp engine. Have had it around for several years mostly sitting. It has always been in a dry warm room just off the shop. It might have 10hrs on it at best. My neighbor kid came over the other day and was riding around. He came in and said it quit. I asked him if it was out of gas. His dad filled it and still no start. I went out and to my surprise it had no compression at all. I first looked to see if the sparkplug was still in it. I told them it was most likely a stuck valve. Pulled the valve cover and had the boy pull it over. Sure enough, intake stuck. Pulled the engine, took the head off and pulled the valve. It was so gummed up I couldn't believe it. Punched it out and did a light scrub with an emery cloth rechecked it as it moves smooth and put back together. fired right back up.
I guess what I am saying, if you pick up one of these engines and it has oil with it in the box, toss it and put some good oil in. Maybe it is because it has sat a lot, not sure, just seemed odd as that has never happened to me before.