old johnson outboard questions.

rrw

rrw

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Hi there, I just found this forum, there seems to be a lot of knowledge here. I have a 15 ft 1971 starcraft fishing boat with what I believe to be a 1963 Johnson 40 HP outboard , model # RDS-25D, serial #2339179. Couple questions: what is the best spark plug and gap to run for trolling? I'm not a fan of champions and that's what it came with. I run shaefers 2 stroke oil in at 32:1, but it still seems to foul up when running slow, it runs very good mid to wide open. Is it suppose to charge the battery? Because it doesnt, it has electric start, the static battery voltage is the same when its off or on(12.6). Any other info concerning this motor is greatly appreciated.

Thank you, Ryan
 
W

wilde1j

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Re: old johnson outboard questions.

BRP recommended plugs for your motor is:
40HP 1960 - 1973 J4C .030"

All OMC/BRP motors have been designed to use Champions, and no reason to mess with any others. If you do a lot of trolling, J6C plugs may resist fouling a little better.

Your motor may not have any charging capability.

Not familiar with the oil you're using. If it's not BIA TCW3 certified, you might try a different, certified oil, especially a synthetic oil.
 
JB

JB

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Re: old johnson outboard questions.

Howdy, Ryan.

Welcome to iboats. :)

Your engine is a 1963 40HP.

The original plug was Champion J4J (now J4C), but she will troll better with J6Cs gapped at .030".

OMC (1964) called for a 24:1 fuel mix for all 1963 Johnson outboards. The 1964 (RDS-26) was rated for 50:1. Many guys are running their RD-25s and RDS-25s on 50:1 without ill effect.

If I had a RDS-25 I would be using a 24:1 mix. I think that oiling an outboard is like watering a horse: More than she needs will do little or no harm, less than she needs will kill her.

I have no idea where any recommendation for 32:1 came from, but it was not from OMC.

Fuel should be 87 octane unleaded regular and must be TC-W3 rated outboard oil

I think the RDS outboards had charging coils for battery life, but I cannot say that with certainty.
 
rrw

rrw

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Re: old johnson outboard questions.

Ok, thanks a lot guys for the quick response! My oil is tc-w3 rated and synthetic. I only run it at 32:1 because that's what I run in all my 2 stroke stuff. I always thought that 24:1 was more so because of the quality of oil back in the day. I will run the jc6 plugs. Thanks again!
 
rrw

rrw

Petty Officer 2nd Class
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Messages
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Re: old johnson outboard questions.

J6c rather, not jc6.
 
kfa4303

kfa4303

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F_R

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Re: old johnson outboard questions.

A DC generator was an accessory at extra cost on that motor. It is a belt driven generator if it has one...easy to tell just by looking.
 
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