1972 Johnson 2hp – low speed and idle problem

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  • July 20, 2015 at 8:36 pm #20483
    fleetwin
    Participant

      US Member - 2 Years

      Stan, you mention that the engine doesn’t look to have a lot of time on it, and no signs of overheating. But, someone may have run it without enough oil and scuffed the pistons/scored the walls. Again, please don’t rip the engine apart based on my evaluation of your compression readings, many gages give inaccurate readings on engines like this with small combustion chambers.
      The easiest test at this point would be to just try another carb, but I’m sure you don’t have one handy. You mention having another look at the throttle plate, so I will assume it hasn’t been messed with, isn’t sticking, and closes all the way at idle. Did you try feathering the choke on and off at lower speeds to see if that helped keep the engine running like Pappy suggested?
      Are you sure the engine isn’t losing spark at low speed?
      In any event, I guess it isn’t a big deal to pull the head and exhaust cover on this engine, provided it hasn’t been used in salt water.

      July 21, 2015 at 3:24 pm #20540
      cajuncook1
      Participant
        quote fleetwin:

        Just want to make sure I understand. You ran the engine before replacing the seals, and it did not idle correctly then either. Am I correct?
        I have never done a compression test on one of these 2hps, but others have reported much higher compression readings, like 115PSI. Any signs of overheating? Have you had the cylinder head/exhaust cover off? Please don’t rip it apart based on my questioning though, hopefully the problem is a much simpler one like others have described.
        I will just emphasize what others have said so far. Make sure the carb butterfly is closing fully, and the throttle shaft is not jammed/corroded. The only way to do this is to remove the carb and look at the butterfly while manually opening the butterfly slightly, then releasing it. The butterfly should snap closed on its own, without having to “help it”. Have a look at the throttle plate as well, does it look like someone has been at the screw/removed it before?

        I agree with Fleetwin, compression on those little motor need to 100psi or greater to idle at low range. You maybe only able to run at higher speed due to low compression.

        I got one off eBay about 5 yrs back for real cheap. Compression was 90psi. It would not idle well. I used some Seafoam in the fuel mix while running and it decarboned it. It jump up to 115psi. I was lucky it was just carbon causing poor ring sealing.

        I sold it a year ago on eBay for about $300. I would always add Seafoam to the fuel mix and it kept it decarboned and the highest psi I got on that motor was 118. Seafoam will not improve compression if the rings and cylinders are worn from a lot of use or poor fuel oil ratio.

        A higher fuel oil ratio like 24:1 might improve ring sealing and get a slightly better psi for lower idling.

        Here is video of 1972 2hp Johnson I sold on eBay. Yeah I know I talk too much in the video.

        http://youtu.be/dfSbAsRDyPE

        Hope this helps some. Cheers!

        David T.

        July 23, 2015 at 10:49 am #20685
        enrico-italy
        Participant

          Hi. I had the same problem with my 1981 Mate 2 hp.

          The probelm was, in my case, a complete obstruction of the low speed feed duct under the float chamber, due to gummy and cristal fuel deposit.

          Check it.

          I need to remove the external lead plug and completely redrill the duct.

          July 23, 2015 at 6:02 pm #20713
          stan-k
          Participant
            quote cajuncook1:

            quote fleetwin:

            Just want to make sure I understand. You ran the engine before replacing the seals, and it did not idle correctly then either. Am I correct?
            I have never done a compression test on one of these 2hps, but others have reported much higher compression readings, like 115PSI. Any signs of overheating? Have you had the cylinder head/exhaust cover off? Please don’t rip it apart based on my questioning though, hopefully the problem is a much simpler one like others have described.
            I will just emphasize what others have said so far. Make sure the carb butterfly is closing fully, and the throttle shaft is not jammed/corroded. The only way to do this is to remove the carb and look at the butterfly while manually opening the butterfly slightly, then releasing it. The butterfly should snap closed on its own, without having to “help it”. Have a look at the throttle plate as well, does it look like someone has been at the screw/removed it before?

            I agree with Fleetwin, compression on those little motor need to 100psi or greater to idle at low range. You maybe only able to run at higher speed due to low compression.

            I got one off eBay about 5 yrs back for real cheap. Compression was 90psi. It would not idle well. I used some Seafoam in the fuel mix while running and it decarboned it. It jump up to 115psi. I was lucky it was just carbon causing poor ring sealing.

            I sold it a year ago on eBay for about $300. I would always add Seafoam to the fuel mix and it kept it decarboned and the highest psi I got on that motor was 118. Seafoam will not improve compression if the rings and cylinders are worn from a lot of use or poor fuel oil ratio.

            A higher fuel oil ratio like 24:1 might improve ring sealing and get a slightly better psi for lower idling.

            Here is video of 1972 2hp Johnson I sold on eBay. Yeah I know I talk too much in the video.

            http://youtu.be/dfSbAsRDyPE

            Hope this helps some. Cheers!

            David T.

            Thanks David and Fleetwin. It looks like low compression is the root cause of my problem too. I had originally got a wrong reading on the compression test. It’s actually only about 60 PSI. So Pappy’s original suspicion was correct. I just removed piston rings and measured the ring gap in the cylinder and wow! about .040" gap when it should be .015" max. The cylinder appears to be in good shape.

            Now to hunt down some rings and a head gasket.

            I just priced them here in Canada…rings $30 CN ($23 US) and head gasket $8 ($6 US)

            Is that a decent price?

            Stan

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