21 yr old Husqavarna 51 has been sitting around most of the time for 6 years. The pull cord assembly is good but takes a tremendous amount of effort to pull it 6 inches. It’s not the safety arm or the clutch. With the plug removed it’s smooth and easy. Has about 1/64 buildup on top of the piston. Internet sources say it’s very common but no one ever claims to have ever truly fixed this particular problem. I think the engine needs to come apart for cleaning and inspection. Anyone fixed one like this, very high compression?