Spark plug replacement question

eprintz06

Recruit
Joined
Feb 2, 2014
Messages
3
Hi Everyone,

I just picked up my "new" boat and am excited for summer to get here. I'd like to put some fresh spark plugs in.

I have a 1999 Johnson 115HP outboard. The service manual for this motor suggests a champion spark plug (QL78YC, gap at 0.030in). When I look on the champion website, the gap listed for these plugs is 0.022-0.028 in.

I noticed that the previous owner had different plugs in there, champion QL77JC4. Looking on the champion website, the gap for these plugs is listed at 0.028-0.033.

Soo, my question now, is why the service manual would recommend a plug that has a gap less than the gap recommended in the manual? Or, are these plugs so close to the same that it doesn't really matter?

Thanks,
-Eric
 

Vic.S

Rear Admiral
Joined
May 4, 2004
Messages
4,690
the recommended plugs are QL78YC and the gap recommended by OMC is 0.030"

QL82YC are often listed as alternatives to QL77JC4. Presumably QL78YC are a little cooler
 
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