In my salt-water area I sometimes see Lightwins with water passages completely blocked with corrosion. The only solution i to pull the powerhead….remove the cylinder head and exhaust cover and locate and clear all the passages. It’s easy enough assuming things come apart without breaking bolts.
Most likely this will not be necessary on your engine but I have attached a picture of the passages. I wish I knew who to credit this picture; I have had it for years after downloading it from one of the forums.
Good luck; don’t run it until you are confident that it is cooling adequately.
