TOPIC: Merc 500 spark plugs

Hope someone can clarify the proper spark plug to use in my 1967 Merc 500 serial #2167849. I have three 500s (ss models), all with different plugs - all with surface gapped plugs. The motor I'm concerned about has Champion L20V plugs installed - A slightly later motor has Champion L78V. While the 1966 500 has AC V40FFM plugs. Unfortunately I have no history on any of the engines (don't even know if they will run). Why I have three engines is another story, suffice it to say that my wife is probably right - outboards seem to breed like rabbits. I figure you guys will understand that part.

I have located sources on the web that say that Champion L76V is correct and others that say the AC40FFM is. Anyone know for sure? The L20V plugs look like they were running too cold, the L78V plugs on the backup engine are new but I'm afraid they may be too hot to use. Even though all of these plugs look to be in good shape, I'll buy new if needed to get the right heat range.

I've picked the engie with the best compression to make the primary and the others will be for parts. Figure it is best to get started with the right plugs.

Thanks for any input, Bill

Bill;
The champion L76V is what Mercury used from the factory. The ACV40FFM is just the AC version of the L76V either one would be fine. I generally use NGK plugs their # would be BUHW Any of the above would work fine. Use which ever brand is available in your area
Tim

Thanks for the help Tim