To clean the valves, I used Easy-Off oven cleaner. Spray them and put them in a ziplock bag and let them soak. Easy-off will break through the carbon.
Get a piston ring tool. Original Yamaha rings and most older piston rings were all made of iron and break very easily. You will have the same problem when you install new rings. Get the tool.
Get a piston ring tool. Original Yamaha rings and most older piston rings were all made of iron and break very easily. You will have the same problem when you install new rings. Get the tool.