50s Johnson sparkplug?

[ryanjames170]

Dose anyone have a chart that shows what sparkplugs the 40s to 50s OMC models take. So I can get the right plugs for some of my motors.

[Anonymous]

The Old Outboard book has two charts in the back of the book. Could you list what motors you need info on ?

[outbdnut2]

Just about all 1950s OMCs used Champion J6J plugs. Today’s offering is a Champion J6C. The C stands for Copper electrode. When you get into the 1960s, the bigger motors (40 HP up) mostly used the cooler J4J.

I sent you a PM with more info.
Dave

[garry-in-michigan]

For Antiques – – – 🙄

[ryanjames170]

good thing is just bought a bunch of J8C’s and J6C’s got 14 and 24 respectivly for the H10 as i think my FD10 takes H10’s could i sub in j8C’s as i see they are between J7J and J8J and people have for other motors said to sub in j8’s for them.

[chris-p]

No. Keep the J8Cs out of them. Too hot.

As stated before, for 50s OMCs, in general use J6C or if you can find them J6J. Not sure what H10s are , never seen them in a motor before.

[ryanjames170]

My FD10 has H10s and I seen they were listed for a few engines.

[dan-in-tn]

I did notice the H10 & H9 plugs have (t) note that says they are 7/16" reach threads. That might make them stick thru the head too far? You would not want the edge of the threads in the combustion chamber. I agree they are up the heat range a bit too far! Might be good for trolling only?
Easy enough to make "C" plugs into "J" plugs. Just file the ground strap back until it only covers half of the center electrode. You then have the old "J" style plug.

Dan in TN

[chris-p]

Your motor of course and you can do what you want, but they are not recommended for any of the 50/60s OMCs. I would toss them out. I pop old plugs in some motors for storage if I don’t have proper ones around. THat may be why you found them.

[ryanjames170]

i think i might know the reason for the H10’s but then leads to to wondering what is up with the throttle.

[Author]

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