Overall Inspection and Spark Plugs

• 1). Visually inspect the motor for obvious leaks, loose connections, missing components or obvious damage. Make needed minor repairs before you proceed, particularly on motors with a high pressure fuel system, like Mercury's Optimax series of motors.
  
  
• 2). Remove the spark plugs with a spark plug wrench and screw the compression gauge into the No. 1 cylinder. Shift the motor into gear and crank the engine for a few seconds with the throttle wide open. Record the reading and repeat the procedure in on the next cylinder. The compression in each the motor's cylinders must be within 10 percent of the compression in every other cylinder. Compression outside this range in one or more cylinders indicates the motor needs an overhaul, not a tune up.
  
  
• 3). Pick up the spark plugs that you removed for the compression test. Inspect the plugs for evidence of oil or carbon buildup, damage to the center or ground electrode -- the tip -- of the plug from improper detonation, and the body of the plug. Record this information, as you may find it useful in diagnosing an ignition system "ailment" at a later date. Put in new plugs: no amount of cleaning and adjustment will match the performance of new spark plugs.
  
  

Filters, Fuel System and an Oil Change

• 1). Remove the serviceable filters and clean them according to the manufacturers directions. If yours is a four-stroke motor, set an oil drain pan under the motor and drain the crankcase oil. Replace the drain plug and fill the crankcase to the recommended capacity with new oil. Replace the inline fuel filters and the fuel pump cartridge filter, if your motor is so equipped.
  
  
• 2). Complete a thorough inspection of the fuel system's hoses and components. Replace any damaged or deteriorating hoses with Coast Guard-approved hoses of the appropriate class.
  
  
• 3). Pressurize the fuel system with the primer bulb and check the lines and connections for leaks. If your motor is equipped with electronic fuel injection, turn your ignition switch to the "On" position. You'll hear the electric fuel pump run for a few seconds and shut off; turn the switch off and begin the inspection.
  
  

The Lower Unit and Final Check

• 1). Remove the propeller and remove any fishing line or marine lift from the propeller shaft. Inspect the propeller shaft seal for damage. Inspect the propeller for nicks, cracks or other damage. Replace the propeller or slather white marine grease on the propeller shaft and send the propeller to a propeller shop for repairs by a licensed technician.
  
  
• 2). Place an oil receptacle under the gear case and remove the drain/fill plug on the bottom of the gear case with a screwdriver. Fell the tip of the plug; it contains a permanent magnet that will attract any bits of ground gears. Bits no larger than a small grain of sand are acceptable, but larger bits indicate the gears need a professional overhaul. Remove the vent plug and drain the gear case oil.
  
  
• 3). Inspect the oil as it comes from the gear case. A milky color indicates the presence of water, which means your propeller seal is damaged and requires replacement. After the oil completely drains, insert the spout of a tube of gear lube into the drain/fill hole and squeeze lubricant into the gear case until it comes out of the vent hole. Screw the vent plug back in, pull the lubricant tube out and screw the drain/fill plug back in.
  
  
• 4). Go boating with your family or friends. Take note of the performance of the starting, fuel, oil and cooling systems and make any minor adjustments as necessary.