1970 25hp johnson.

J

jdt

Seaman Apprentice
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May 11, 2007
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38
Hello,
I recently purchased a used aluminum boat with a 25 hp johnson on it. I am going to order a manual but wanted to get started with it. What fluid do I put in the lower unit? Is it regular 80-90 weight?
Thanks
 
samo_ott

samo_ott

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Jun 18, 2006
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5,125
Re: 1970 25hp johnson.

Yes, it's regular lower unit oil. OMC sells the stuff, so does Wal Mart I hear. Make sure you use new washers around the screws when you replace it. They are cheap and important. And it's a 50:1 fuel/oil ratio with tcw-3 oil.

It's also a good idea to check the compression on a new to you engine for a baseline but not essential if it's running ok. Is it?
 
J

jdt

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May 11, 2007
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Re: 1970 25hp johnson.

Ok. Thanks for the info. I have just started it up in the barrel at the place I bought it. It just ran maybe a few minutes. Seemed to run ok. I have to get the lower unit fluid changed and the boat and trailer liscenced and then I will put it in the water and let it run abit and see what happens. Is the hole on the back of the shaft an exhaust hole? It is about half way up. Any other advice or information is great and would be greatly appreciated.
Thanks,
Jdt
 
tashasdaddy

tashasdaddy

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51,019
Re: 1970 25hp johnson.

the hole is an exhaust relief port for when idleing, you should also get a mist or droplets of water out there. watch the temperature, if it gets to where you cannot hold you hand on top of the block for 3 count the motor is hot,
 
J

jdt

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Re: 1970 25hp johnson.

Understand 3 count and then hot. I will make sure and check that. So most of the water comes out the prop then right? Just a few spitz and and a mist out of the relief hole. It looks like a decent little motor. Oh, 1 more question.......is there sposed to be something right in front of the carb? It looks like anything can go into the butterfly carb opening......there is like an 1inch or so space before a plate. Just wondering. I figured there should maybe be something there.
Thanks again for the knowledge!
Jdt
 
CATransplant

CATransplant

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Re: 1970 25hp johnson.

Some outboards have a silencer box mounted in front of the carb, but most don't. Yours did have a silencer as standard equipment. Its cover is where the choke and other junk come out the front. You might not recognize it as such.

On my old 35hp Johnson, the carb just had a coarse screen. I figured if the black flies got bad enough, I could take the cowling off and let the carb suck them down and burn them up. :D

You can go here, then drill down to your model and select Carburetor Group to see the parts explosion showing the silencer:

http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f
 
J

jdt

Seaman Apprentice
Joined
May 11, 2007
Messages
38
Re: 1970 25hp johnson.

OK, thanks. It looks like I am missing the silencer pad and plate. #39 & #40. Are these peices important? I would think so. I will check around and try to find them.
Thanks,
Jdt
 

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C

ColdPat

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May 20, 2007
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35
Re: 1970 25hp johnson.

I have a 1975 25hp johnson. My carb looks just like that. I would take it apart and put new gaskets. I would soak the bottom of the bowl with carb cleaner then blow out the hole for the low speed fuel. This hole starts at the bottom of the bowl and then comes up the side of the bowl. This hole gets gumed up sometimes and this is where people say won't idle but runs great at higher speeds.

This is a awesome little motor. I plan on buying another jon(wider) and keeping this motor because it is so easy to work on
 
J

jdt

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Joined
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Messages
38
Re: 1970 25hp johnson.

Re-examining the carburator area and the diagrams.....it looks like there is a screen and a pad in the screen cover so maybe it is normal on this to have that much gap between the butterfly and the screen? Any thoughts?
Thanks,
Jdt
 
C

ColdPat

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May 20, 2007
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Re: 1970 25hp johnson.

Yes,
My carb looks identical to your pics. ie spacing between plate and carb.
 
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