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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