Spark plugs

[Boonie]

Working on several resto models right now.
Johnson RD10
Johnson QD12
Evinrude 3 hp lightwin
Mercury KD4
What are the spark plug recommended #’s for each model? Preferably champion.

[Buccaneer]

OMC
3 hp 1952-1968 Champion J6C 0.030 gap

10 1952-1958 J6C 0.030
10 1959-1963 J4C 0.030

25 1952-1955 J4C 0.030
25 1969-1976 J4C 0.030

Prepare to be boarded!

[Bob Wight]

Champion plugs

RD10 – J6C
QD12 – J6C
Evinrude Lightwin – J4C
Mercury – don’t know

I’d suggest you would do better using NGK plugs, B6S for the Champion J6C and B8S for
the J4C.

Edit – I used a Johnson Motor Spec sheet from 1960 to come up with the Champion numbers.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

• This reply was modified 4 years, 2 months ago by Bob Wight.

[chuckw]

Mercury: B6S NGK plugs or J8C.

• This reply was modified 4 years, 2 months ago by chuckw.

[fifty20ne]

The correct Champion
Spark plug for the
Mercury KD-4 is a
Champion J-7j gapped
At .025

Peter Hunn’s book

“The Old Outboard”
Has all spark plug
Listings in back of
Book pages # 296 – 299
Good book! I have the
3rd edition
Can be found new on
Amazon or used on EBay
Etc…

[Boonie]

Just purchased the old outboard from Amazon. Thanks

[Author]

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