Just keep tuning for optimum performance, you may need to start adding 2 washers to the glow plug to stop the piston from hitting it. You can check your engine, just by taking off the cooling head, and turning the flywheel. If your piston comes all the way to the top of the sleeve it is shot, but since you have had it for years, and many gallons through it, just keep tuning and running until it wont stay running anymore.