To maintain performance and peace of mind, a tune-up of your marine engine should be performed on a yearly basis. These high quality, do-it-yourself kits include cap, rotor, points, and condenser. Complete your tune-up by changing your spark plugs and plug wires. For Mercruiser V-6 engines with Thunderbolt IV ignition systems. Thunderbolt IV ignition systems | Aqua Power Complete Performance Marine Tune-Up Kit, Mercruiser V-6 Engines