Johnson PO-15 Spark Plugs?

[Buccaneer]

Trying to figure out what 18 mm spark plugs to order for my 1950
Johnson PO-15. I’m told the later model PO’s may take
a different plug than the early ones.

I need the style plugs that have the threaded tops so they
will work with the "eyelet" style spark plug wire terminals.

Thanks for your help!

Prepare to be boarded!

[garry-in-michigan]

The original Champion R7 has been replaced by champion 506. I like to file pack the side electrode to center of the center electrode. This converts them to the "- J" two cycle type. . . 😉

[Buccaneer]

Garry, thanks for the reply. Some of the EBay listings state
that the Champion 506 is a "Resistor" style plug.
Is that a "no no" for old magneto outboards?

I found this Champion Chart. The non resistor equivalent
is shown as D6, the "coldest" in the group.
It’s frustrating looking for D6 or D9 plugs, as they
always show up with the non-resistor number 506 or 509,
listing D6 or D9 as equivalents. Of course EBay doesn’t
show the actual number on the plug you’d be buying 🙄
The chart also shows three different "reach" plugs….
not sure what’s needed for the PO.

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Attachments:

Prepare to be boarded!

[outbdnut2]

I’m running Champion D9s (509) in my late 1940s PO15 and it runs great.

Amazon has them:

https://www.amazon.com/Champion-509-Ind … B000B7RCMG

My PO15 was starting hard when it got warmed up and I was thinking spark plugs, but I found that even if it had just been run, if I hold the little primer button down until gas comes out the small tubes, it starts right up warm with the D9s.
Dave

[garry-in-michigan]

Spark plug "reach" is the distance it screws into the head. Using too short a reach will recess the contacts and may strip the threads in aluminum heads if over torqued. Too long may hit the piston, closing the gap, or worse. . . 😮

[Buccaneer]

Dave, Do your plugs say D9 or 509 on them? How can they call
them the same number if one is resistor and the other non?
At any rate, if they work good in yours, I’ll order some. Thanks!

Garry, I’ll measure the thread "reach" on the head to see ! Thanks.

Prepare to be boarded!

[outbdnut2]

quote Buccaneer:

Dave, Do your plugs say D9 or 509 on them? How can they call
them the same number if one is resistor and the other non?

.

I don’t remember how the plugs were marked, and I cant get to the motor until spring because of boats stored in front of it, but if you look carefully at the Champion chart you posted, D9 and 509 are different numbers for the same plug, and it is not a resistor plug. The resistor plug column to the right on the chart shows a RD16 as the only resistor plug in that "D" series.
Dave

[Anonymous]

D6 is marked on the plug, but if you look in the Champion catalog a D6 is a stock number 506. D6 on the plug and Champion calls it a stock number 506. D9 is stock number 509. I use D6 plugs in my PO motors, which is the current closest plug to the Original R7. The D6 is slightly hotter than the R7. And the D9 is a little hotter than the D6. After running D6 plugs in your motor check the color and if they are very dark brown to black tips then try D9 plugs to get a medium brown colored tips.

[outbdnut2]

Remember the gas/oil mix for the PO-15 is 8 to 1, and amazingly, it doesn’t smoke hardly at all! I just mention it in case the decal onthe tank is damaged and not readable. Note that the Champion "Hotrod" racing motors ran a 4 to 1 gas/oil mix.

Dave

[Buccaneer]

Well I think I removed all doubt…… "I must be cross-eyed and lysdisic" !
I see now that there is only "one" resistor plug in the chart.
The power of suggestion must be strong, as someone on EBay was advertising
their 509’s as "Resistor" plugs.
I long for the good old days…… put a J-8 in something and you were good to go, lol.
Thanks for setting me on the right path!
Regarding the oil mixture ratio, what I got from reading the 1970’s archived
articles on the Johnson PO-15’s were "3/4 pt / gallon oil to fuel mixture recommended, or more for heavy use",
which was probably what the writer’s belief, and not Johnson’s.

Prepare to be boarded!

[Author]

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