Johnson 25HP plug question.

MicroBoat

Recruit
Joined
May 14, 2004
Messages
5
I bought a fishing rig last fall &, of course, took her for a test spin before I bought it. The<br />'90 25HP Johnson purred like a kitten. When I was putting new plugs in this spring, I noticed he hadn't been running the recommended plug in it.<br />This engine is supposed to take QL77JC4 gapped at 0.030". What was in there was NGK BR4HS gapped at 0.025". This plug isn't even the NGK equivalent of the Champion plug. My question is why does the motor run better on this maverick plug than with the Champion plug that it calls for? :confused:
 

seahorse5

Rear Admiral
Joined
Jan 24, 2002
Messages
4,698
Re: Johnson 25HP plug question.

The NGK is a much hotter rated plug than the QL77JC4 and could have possibly caused internal engine damage. There are 3 factory recommended plugs for that motor according to the Bombardier book. One is the QL78 which is a surface gap for commercial use at high speeds. The best all around plug is the recommeded QL82C gapped at .030". It has more foul resistance than the QL77JC4.
 
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