Newby with question

Arky72560

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Joined
Mar 3, 2015
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3
A friend of mine just sold me two Johnson outboards that he used on his boats at one time. The first and oldest in appearance is marked 25 horse, when I run the model # 25R70E, it comes back as a 1970 model 25 hp, the second which says 20 on the cowl has a model number of 10424S, this does not come back to a 20hp but rather a 1974 9.9, he told me that the 25hp ran the best when he used it, the 20 or 9.9 would sort of jerk or shudder when you tried to open it up. I plan on trying to get both working, the 25 hp is what I will work on first as it will be going on my fishing boat. Both motors were loaded with rats nests under the cowl when I opened them up. I have ordered service manuals but can anyone suggest a starting point. I am totally new at this and trying to teach myself a new skill. Also can anyone reccomend any special tools needed to fix and maintain these motors, I assume a compression tester,but beyond that I am clueless, I saw several compression testers on ebay starting at $18 and going up to $100 plus. Is there any particular compression tester or is it a universal tool?
 
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jasper60103

Commander
Joined
Sep 18, 2008
Messages
2,055
Welcome aboard, Arky72560. Compression test is a good start. I would borrow one for free from a local auto parts store. Autozone and Oreillys have free tool loaner programs. Good luck.
 

alldodge

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Mar 8, 2009
Messages
40,582
A friend of mine just sold me two Johnson outboards that he used on his boats at one time. The first and oldest in appearance is marked 25 horse, when I run the model # 25R70E, it comes back as a 1970 model 25 hp, the second which says 20 on the cowl has a model number of 10424S, this does not come back to a 20hp but rather a 1974 9.9, he told me that the 25hp ran the best when he used it, the 20 or 9.9 would sort of jerk or shudder when you tried to open it up. I plan on trying to get both working, the 25 hp is what I will work on first as it will be going on my fishing boat. Both motors were loaded with rats nests under the cowl when I opened them up. I have ordered service manuals but can anyone suggest a starting point. I am totally new at this and trying to teach myself a new skill. Also can anyone reccomend any special tools needed to fix and maintain these motors, I assume a compression tester,but beyond that I am clueless, I saw several compression testers on ebay starting at $18 and going up to $100 plus. Is there any particular compression tester or is it a universal tool?

:welcome: to iboats

^+1 agree and will add. If you do buy one just get one which screws into the sparkplug hole. Don't get one with a rubber ti[ which you hold. The rubber tip ones vary to much based on how hard you hold it. Another nice feature to have is a quick release on the gauge. The release allows easier threading of the hose fitting into the cylinder without the gauge being attached. Either way is fine, just the release makes it easier.

When you get into the rebuild don't forget the pics, we all like pics around here :D
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
There is a huge difference between a 9.9 and a 20/25. The 20/25 are about the same size, while a 9.9 is much smaller.
I don't envy you for the job you are about to confront. Those mouse nests are disgusting. I suppose the first thing I would do is pressure wash it. Protect it so you don't turn the hose into the carburetor opening.
 

Arky72560

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Mar 3, 2015
Messages
3
That is what confused me some, I assumed that there would be a big difference in size but these two motors are nearly identical in size and weight. I double checked with the man that I bought them from, he never looked up part or model numbers on the one marked 20 because he never needed any parts. Whatever the case I paid $150 total for the two motors so I don't think I can go wrong.
 

Arky72560

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Joined
Mar 3, 2015
Messages
3
IMG_20150304_170428.jpg ​Here are some pictures.
 

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jasper60103

Commander
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Sep 18, 2008
Messages
2,055
That is what confused me some, I assumed that there would be a big difference in size but these two motors are nearly identical in size and weight. I double checked with the man that I bought them from, he never looked up part or model numbers on the one marked 20 because he never needed any parts. Whatever the case I paid $150 total for the two motors so I don't think I can go wrong.

Sounds like a good deal. The mice are worth at least that much. :D
It looks like electric start was added to the 25?
Let us know what the compression numbers are. Good luck.

-jasper
 
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