72 7.5 Merc

[rnl]

Someplace I read that the correct spark plug for this engine was a champion L77JC4. I just came home w/a couple and found that the engine had Champion L78V plugs in it These plugs are very different and I would hate to damage the engine with the wrong one. Will the L77JC4 work?

 

[diaric]

Re: 72 7.5 Merc

L77JC4 is for 79-85 7.5 hp
L78V is what old mercs list for a 72 and is a surface gap plug.
champion site lists 5838 for a 72 which is also a surface gap.
so, i wouldn't use the L77JC4

 

[indianamike]

Re: 72 7.5 Merc

I have a 1973 Merc 7.5hp with Phase-Maker ignition. My Clymer's manual calls for Champion L78V or AC-V40FFK surface-gap plugs (some of the newer 7.5s use Champ L77V or AC-V40FFM surface-gaps). When I got the motor, it had NGK BUHW-2 surface-gap plugs, which I assume is equivalent to the L78V. While getting parts for a tune-up, my local Mercury dealer recommended using a conventional plug, and sold me a set of NGK B6S plugs. They said something about better/more consistent spark. These seem to work fine in my motor, but I'm not sure they are any better.

Mike

 

[rnl]

Re: 72 7.5 Merc

Thanx guys. My local Marina had the NGK BUHW on the shelf. They worked out fine thanx for the input.