I've got a Ferris 48" single hyrdo commercial mower with a 13 hp Kawasaki engine. While mowing the other day, the engine started sputtering and at idle it died. Upon inspection, the spark plug boot had come all the way off. I put it back on and finished mowing but the boot just keeps coming off. The boot will slide on the spark plug fine but it's not tight at all. I tried to tighten the coil inside the boot with pliers but it didn't help. Is there a way to tighten this boot or does it need replacement? If replacement is needed, how? Thanks for your help.