Champion QL77JC4 vs. QL78YC

Sand Bass

Seaman
Joined
Jul 17, 2002
Messages
68
What is the difference between these two spark plugs? My manual calls for QL77JC4 but I have noticed more people using the QL78YC in motors like mine and others that call for the QL77JC4.<br />My engine is a 1994 Evinrude 225.<br />Thanks
 

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: Champion QL77JC4 vs. QL78YC

sandbass,The QL78YC plug has a taller electrode and fires a bit deeper in cylinder.Don't know if your 225 calls for it as an optional plug or whether you would experience better operation than with the QL77JC4.My 95 70 rude calls for the YC plug and lists the JC4 as an optional.
 

seahorse5

Rear Admiral
Joined
Jan 24, 2002
Messages
4,698
Re: Champion QL77JC4 vs. QL78YC

Manuals are out of date right after they are printed because manufactures make changes and improvements over the years. Since 1995 the former OMC recommended QL78YC plugs in all loop engines 40hp and up for '94 and later in all their catalogs and service literature.
 

Sand Bass

Seaman
Joined
Jul 17, 2002
Messages
68
Re: Champion QL77JC4 vs. QL78YC

Thanks Seahorse and ob. I will switch to the QL78YC plugs. Seahorse, your knowledge of J/E engines is much appreciated.
 

snard

Cadet
Joined
Jul 16, 2002
Messages
20
Re: Champion QL77JC4 vs. QL78YC

I am using the QL77JC4 as for a 1989 225 Johnson. Should I change?
 

seahorse5

Rear Admiral
Joined
Jan 24, 2002
Messages
4,698
Re: Champion QL77JC4 vs. QL78YC

Angler,<br /><br />Keep those '77 plugs as that is the recommended style. As I posted earlier, the QL78YC plug is for '94 and later motors.
 

Bassnwhaler

Cadet
Joined
Aug 12, 2019
Messages
12
Opening an OLD thread: I have a Johnsonrude 1990 120 looper. Rebuilt in 2020. Does that make it a pre 1994 or post 1994? Not sure which plugs to use.

Thanks!
 
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