1977 Johnson 25hp - Confused on what spark plugs I should be using.

[Ibrettfavre]

The plugs I pulled out are called "surface discharge" plugs and it's the first time I have ever encountered them, they're also really hard to find.
The motor cover says "champion L77JC4", and the plugs I pulled out said "champion L77J4". The J4 plugs are the surface discharge plug, and the JC4 plugs have the electrode like most plugs you see.

My buddy said not to use the plugs with the electrode on that motor because the piston will keep hitting it and eventually tear it up, that would cost me alot as I have pretty much no knowledge when it comes to small engine rebuilds.

I've searched high and low and I can find no information about my situation, also every time I try to research the plugs using the model number of the motor it always directs me to some plugs with electrodes, which leads me to believe it's ok to use them but the boat has always run great with the no electrode surface discharge plugs. "Don't fix what ain't broke" right?

Also, the model number of the 25 hp Johnson motor is 25r277h

Can't post a picture of the surface discharge type plug for reference but here's the url:

https://www.google.com/search?q=cham...0S625MsJ_GgQM:

 

[oldboat1]

The late (Great) Frank Acampora had a good post on the difference between surface gap and bent electrode plugs: http://forums.iboats.com/forum/engi...rd-discussions/464730-surface-gap-spark-plugs . For lower speed running, the bent electrode plugs are probably better, but will be mixed opinion (like on oils).

I think the L77JC4 is indeed the recommended plug for your 25. If using surface gap plugs, you might find that the JC4s give you a little better idle. Gap is .030.

 

[Vic.S]

The latest recommendation for that model is QL77JC4 or QL82C

JC4 are recommended for earlier ('69 to '76) models

QL77JC4 or L78V ( surface gap) or QL82C for '78 to 2001 models

 

[racerone]

Your ---" buddy "---Does not know his motors very well !

 

[Joe Reeves]

Champion QL77JC4 plugs, gaped at either .030 (long life) or .040 (strong spark).

The "Q" indicates a suppressor plug... noise quieter if you're running a depth sounder, radio, whatever. If these do not exist, you can drop the "Q" and us the regular Champion L77JC4.

 

[jimmbo]

I had no problems with the surface gap plugs on a 1980 35hp, or on my 115 merc. The plugs in the merc were still the originals 14 yrs and 776 hrs(hourmeter) later when I traded it in.