1. I just purchaced a tach for my boat, its the System Check OMC Tach. Switch setting on back for 5 or 6 pole. I think it needs to be positioned to 6 but I want to make sure. I have Clymer shop manual and cant find a thing in there about number of poles.2. Manual says spark plug for that motor is QL78YC and the spark plug book at the store said QL77JC4. Which is the correct plug and what is the differance in the 2 plugs?Thanks for your assistance in these matters ahead of time.