Spark plug question 1969 Big Twin 40 hp

[Sport240]

Another day, another question!

Like the title says, i have a 1969 Evinrude Big Twin 40hp (40972R) which I'm bringing back to life. Was heading out the door tonight to go buy spark plugs, which I thought should be Champion J4C, but before I left, I checked what was in the motor right now and found Champion J6C's...

A little surprised, I went here to check:

http://www.ishopmarine.com/ishop/js...CatFilter=BRP&eCatSupFldr=supplier-100-005-EJ

Found out that they suggest J4J's !!!

So what is it? An thoughts? I know nothing about spark plugs (hot, cold, equivalents, etc...)

Thanx again!

JD

 

[boobie]

Re: Spark plug question 1969 Big Twin 40 hp

If you can find the J4J's, put them in as that was the orginial plug. If not the J6C's will work.

 

[HighTrim]

Re: Spark plug question 1969 Big Twin 40 hp

They dont make J4J or J6J anymore, they are called J4C and J6C

It really depends on the amount of trolling you do and such. For general use, the J6Cs are fine

 

[Sport240]

Re: Spark plug question 1969 Big Twin 40 hp

This is where I got the J4C idea...

http://continuouswave.com/whaler/reference/BRP_SparkPlugChart2007.pdf

Whats the difference between J4C and J6C?

JD

 

[steelespike]

Re: Spark plug question 1969 Big Twin 40 hp

The J6C is a hotter plug.I suppose if running slow for extended periods a hotter plug may help keep the plugs cleaner.
But have to be careful if running extended high speed as well.

 

[Joe Reeves]

Re: Spark plug question 1969 Big Twin 40 hp

The original recommended spark plug was the Champion J4J which has been superseded up to the J4C, the "C" standing for copper electrode which lasts longer. OMC recommended the J6C, which is slightly hotter, as an alternative spark plug which may improve performance on older engines (yours). It doesn't matter which plug you choose excepting that one or the other may provide improved performance either at an idle or at full throttle.... it varies from engine to engine. The gap setting should be .030 on either spark plug.

Try both and make a note of the difference in performance if any.

 

[Sport240]

Re: Spark plug question 1969 Big Twin 40 hp

Thanx fellas! You guys are great!