Which spark plugs are the right ones?

[cr9c1]

I have two outboards. 72 25hp and 73 9.5hp. The champion spark plug site says both take J8C. Somewhere else, not sure if its my dealer or not said J6C. I then found a post on here listing all the different horsepower, years, ignition systems, etc, that said both of them take a J4C plug. Anyone help me out?

 

[wilde1j]

Re: Which spark plugs are the right ones?

25 1969 - 1976 j4c .030

9.5 1964 - 1973 j4c .030

 

[cr9c1]

Re: Which spark plugs are the right ones?

Thanks Jim! I take it the J4C is widely available then? I wonder why my dealer always gave me J6C / J8C. My 9.5 seems to run fairly hot even though it is pumping water perfectly and the thermostat is opening when it should, could this be part of the problem?

 

[wilde1j]

Re: Which spark plugs are the right ones?

J6C is a hotter plug than J4C, and may work better if you spend most of the running time trolling. I would be somewhat wary of using J8C.

 

[cr9c1]

Re: Which spark plugs are the right ones?

Well typically I don't troll at all. In fact, the only time I'm really going trolling speed is in and out of the dock or the camp. I would like to avoid spark plug fouling, however. I'll give J4C a try and see how it works. If I begin having problems, I'll switch up to J6C.

Appreciate the help as awlays.

 

[RSchendel]

Re: Which spark plugs are the right ones? '58 18hp

Re: Which spark plugs are the right ones? '58 18hp

I have the almost identical dilemma. I have a '58 Evinrude 18hp 15024.

Original Parts Manual specifies Champion J6J.
New substitute for J6J is J6C according to Champion site.
Champion Application Guide indicates J8C.

Other posts on this site and others specify J4C. My motor currently has J4Cs installed, but they are a bit black. I have no idea how long they have been installed as I just acquired the outboard.

I am inclined to try the J6C as the heat range is between the two others.

Also, is there any harm in using Resistor plugs to prevent interference with my depth finder?

 

[JB]

Re: Which spark plugs are the right ones? '58 18hp

Re: Which spark plugs are the right ones? '58 18hp

The applications guide is loaded with errors.

Both of your engines, as indicated above, run best on Champion J4C and troll for long periods best on J6C. Either gapped at .030".

 

[seahorse5]

Re: Which spark plugs are the right ones? '58 18hp

Re: Which spark plugs are the right ones? '58 18hp

I have the almost identical dilemma. I have a '58 Evinrude 18hp 15024.

Original Parts Manual specifies Champion J6J.
New substitute for J6J is J6C according to Champion site.
Champion Application Guide indicates J8C.

Other posts on this site and others specify J4C. My motor currently has J4Cs installed, but they are a bit black.

A rule of thumb for 50 year old and older Johnson and Evinrudes is to use the J6C plugs in outboards without a thermostat, J8C plugs in cold water conditions or extended low speed operations.

In thermostat equipped motors, J4C plugs are recommended. J6C works great if fouling problems occur.

The newer factory charts are not accurate for those motors over 50 years. If the decals on your motors are still readable, go by those recommendations.

Plug numbers changed over the years - J6 and J6J plugs are now J6C - same with the J4J and J8J numbering.

 

[F_R]

Re: Which spark plugs are the right ones? '58 18hp

Re: Which spark plugs are the right ones? '58 18hp

Resistor plugs require more voltage to fire them. That is voltage that you have to generate when you pull the rope. Also voltage that generates while it is running. So, bottom line is resistor plugs might cause hard starting or poor running. If it starts and runs ok with them, no problem. But the opposite is usually the case.

 

[RSchendel]

Re: Which spark plugs are the right ones?

Thanks...I appreciate the responses.