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Johnson 4hp no power

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  • Johnson 4hp no power

    Hello, I stumbled across this forum while searching for informatiion about my motor. It's a fantastic site and I really admire the people who take the time to answer questions and give advice to amateurs like myself. I hope i'll get my questions answered too. I bought this Johnson 4hp from mid 70's and used on a square stern canoe to go camping in weekends in far places. it worked perfect for half a dozen trips. One time I pulled another heavy canoe as well for about 5 hours. The motor ran perfect under stress; it did not seem to overheat or anything. However, last time I used it it ran well for 15 minutes after which it stalled. After that it would only run at low rpm; as soon as I'd give it more gas it would get rough and eventually stall. I pumped fuel manually using the hose bulb, thinking it wasn't getting enough gas. Did not help. After a while it stopped working completely. Half a year later I'm trying to fix it. I was planning on cleanning up the carburator, thinking that the high speed jet is clogged. I haven't got so far yet; unscrewing the spark plugs I noticed that one of them is covered in oil. Now I'm thinking that maybe the head gasket might be blown. Before I go buying unnecessary parts and frustrating myself, can anyone offer some clues as to what my problem might be? Thank you very much, advice like this is great value to anyone.


  • #2
    Re: Johnson 4hp no power

    I agree with you that it may be a clogged carb. To check, try spraying oil/gas premix into the carb throat when it's running to see if it starts.

    To fully troubleshoot systematically, you'd run a compression check, spark test, then if those were both OK then you'd know it was in the fuel system.
    Please no PMs. My mailbox is full anyway......

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    • #3
      Re: Johnson 4hp no power

      What is the model number of the motor?

      Comment



      • #4
        Re: Johnson 4hp no power

        The model number is 4W72S and the serial number is C40065.

        There is a film of burnt lookin oil around the bottom part of the cylinder block as well (not sure I'm using the right terminology).

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        • #5
          Re: Johnson 4hp no power

          A compression check will show if you have a bad head gasket.
          Please no PMs. My mailbox is full anyway......

          Comment



          • #6
            Re: Johnson 4hp no power

            Thats a 1972 motor. You need to pull the flywheel and check the coils for cracks . If you have never gave it a tuneup new points and condensers would help also. Maybe check the carb for debris and install a kit if needed,Also change the fuel line's the older fuel lines will deteriorate from the Ethanol in todays gas

            Comment



            • #7
              Re: Johnson 4hp no power

              Based on what the guy I bought it from told me, the motor ran for less than 40 hrs since the last tune up 3 years ago. Hoses, plugs and everything inside look sparkling clean/new, apart from this oil stain I noticed after the mishap.

              If I' going to do it myself I guess I'm gonna need a manual to identify coils, points, etc.

              This may sound stupid, but I guess you can't do a compression test at home without some specialized equipment, right?

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              • #8
                Re: Johnson 4hp no power

                Auto Parts stores sell compression gauges fro around 25.00 dollars check here for the parts breakdown

                http://shop2.evinrude.com/ext/index....117be584b610a1

                Comment



                • #9
                  Re: Johnson 4hp no power

                  Thnak you both, whaler and defiant! I guess an owner manual will tell me how to use the compression gauge and what it should read for my motor model.

                  My understanding is that there can be a number of different causes for my motor's malfunctioning and I need a systematic approach, starting with a compression test, spark test, coils, condensers, carb cleaning, etc. and that I would eventually need to get a manual and a number of tune up kits. Unless I decide to take on an a new hobby, I should probably go to the nearby marina shop .

                  Thank you both for taking the time to answer my post.

                  Comment



                  • #10
                    Re: Johnson 4hp no power

                    With a Manual you should be able to do it yourself and save some money.

                    Comment



                    • #11
                      Re: Johnson 4hp no power

                      Originally posted by dirtyhands View Post
                      Based on what the guy I bought it from told me, the motor ran for less than 40 hrs since the last tune up 3 years ago. Hoses, plugs and everything inside look sparkling clean/new, apart from this oil stain I noticed after the mishap.

                      If I' going to do it myself I guess I'm gonna need a manual to identify coils, points, etc.

                      This may sound stupid, but I guess you can't do a compression test at home without some specialized equipment, right?
                      Some auto parts stores loan out compression gauges for no money. AutoZone does that around here.
                      Please no PMs. My mailbox is full anyway......

                      Comment

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