I have just resurected a twenty year old OS FS 20 Four Stroke. It as completely frozen up, but by disassembling and soaking it in penetrating oil, I got it to turn over smoothly. The biggest problem was freeing up the tappets, as the cams were hanging up on them.
The engine started right up and runs fine at full power. The only problem is that when I throttle back to half power or so, the engine will only run for about five seconds and then lean out. I noticed that when I disassembled the carb that there appeared to be white silicon sealant around the rotating barrel on the throttle arm side of the carb. I suspect that I may have to replace the sealant to keep out air which apparently is causing the engine to kill lean.
Does anyone have any thoughts? Thanks. Stewbow