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spark plugs for 1968 Johnson 3HP

L

LRM2

New member
Hi all,
I just bought a JW-23A. Seems in good shape. I didn't measure compression, but pulling the starter seems pretty tight. I've cleaned the carb (and have a kit on order), replaced the internal fuel lines, and the fuel pump looks to have been recently rebuilt. But there's no spark. One of the points is set with no gap at all - jammed tight closed - so that's clearly a problem. I'm replacing the points, condensers, spark plugs and spark plug wires. Coils are the green and purple ones, and test good. I've ordered new ones to have on hand, but I think for now I'll use the old ones.

For the plugs, it seems like Champion J4C is the standard reference. Easy to find and reasonably priced. There are something like 115 cross references for this plug. Is there any reason to use a different plug?
Thanks!
Lewis
 
The rule used to be----With thermostat J4J ( J4C ) and without thermostat like your 1968 model J6J ( J6C ) ------These are a sweet little motor.----Install a new impeller now if you do not know how old it is.
 
Thanks, Racerone. A new impeller is definitely on the list. I bought the motor as a short shank weedless, and am converting it to a long shank non-weedless. So a few steps to go before the impeller ;)
 
I have bunch of old boats and outboards, and I find eBay to be a great resource. For this one, I found a lower unit from one eBay seller, an extension piece from another, a driveshaft from a third, etc. Not as convenient as a perfect match donor, but not bad at all.

MarineEngine.com has a water tube extension, so I ordered that. If I remember correctly, the water tube on this motor is just a piece of 1/4 inch copper tubing. If that's right, I may just make a new longer one rather than using an extension.
 
racerone said:
The rule used to be----With thermostat J4J ( J4C ) and without thermostat like your 1968 model J6J ( J6C ) ------These are a sweet little motor.----Install a new impeller now if you do not know how old it is.
Click to expand...

Sorry I drifted a bit off topic. The J6C fires a little hotter than the J4C, is that correct? What is the rationale behind using the 6 vs the 4? Please understand that I'm not questioning your expertise; I'm just trying to learn.
Thanks,
Lewis
 
No sparkplugs do not ---FIRE HOTTER---------It has to do with dissipating the heat away from the plug.-----So a motor without a thermostat may run cooler.----Therefor you need a plug that stays warmer to a degree !
 
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