Merc 500 50 hp What Spark Plug??

[TominatorNY]

Ok so I thought it would be EASY to put in new plugs... what was I thinking? Merc 500 1970 ser#2742087 Thunderbolt ignition. Has L78V plugs now, but I know that was a replacement form whatever the original was. I read some old posts on here that say L78V is too hot, they say use L77V... so I went to oldmercs.com, they say use L76V. Still other posts on here suggest changing from the flat-point plugs to a standard gap plug... I'm certainly not a spark plug expert, does anyone on here know more about these type of plugs?

 

[tmcalavy]

Re: Merc 500 50 hp What Spark Plug??

Go with the L76V recommended by Mercury. Your outboard is also made for surface gap (flat) plugs. Saw some just yesterday at Wallyworld on the spark plug rack. Keep and extra set around.

 

[TominatorNY]

Re: Merc 500 50 hp What Spark Plug??

Whats your reasoning for choosing the L76V?<br /><br />Anyone else have an opinion also?

 

[Greg New Zealand]

Re: Merc 500 50 hp What Spark Plug??

I was running L76V plugs in my 4cyl 50. I recently changed over to NGK BUHW and the motor is running a lot better. I have read that Mercs like NGK plugs - OMC like Champions. Don't know why.

 

[tmcalavy]

Re: Merc 500 50 hp What Spark Plug??

Reason for choosing the L76V plugs is they are listed as the plug of choice in the Merc service manual for my outboard. Haven't tried the NGKs, they may be just as good.