There is no plug to start the engine. This is an important part and is essential for maintenance. Even if it looks no abnormalities, you dont have to worry about the engine because of the plug. It is better to replace the plug once a year. Sometimes you may need to replace it in the ocean. Therefore, it is recommended that you always have the number of plugs used on your boat. Please make sure the plug is compatible with your engine. You may not be able to run out of power or damage the piston. Please note that there are absolutely no problems with engines using incompatible plugs.