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1978/1981 Evinrude 115hp Carb/Ignition Problem

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  • 1978/1981 Evinrude 115hp Carb/Ignition Problem

    Rebuilt 1978 motor with all other parts off the 1981 original motor. Okay I have 3 spark plugs that are kinda wet and one that is dry but medium brown color. Problem is engine is not running full RPMS like 4800 vs 5400... Use to cut in and out now it just stays out of full power. I have bought a new fly wheel and stator and will have that installed in Dec. But meanwhile I am messing around. I have today replace those blue spark plug wires with the original OMC spark plug wires. Now I have the carbs off and will start cleaning them tomorrow. I am thinking about buying all new jets, and according to book. they would be sizes 28, 34, and 60.. My manual is an original manual so what I would like to know is if those jets sizes are still valid before i order them. Thanks in advance. Oh spark looks okay, compression is around 110 on all 4 cylinders.

  • #2
    In essence, you've built one engine out of two engines and we have no idea if the parts you're using may have a slight design difference, the wrong jets, whatever... so you're more or less on your own in many areas. Such as in the case of carburetor jets, you'll need to look them up here in the forums parts list, a factory parts manual if you have one, other forums, etc.

    However, the spark looking okay and the compression being around a certain number doesn't cut it..... you need to be precise as in.................

    Compression: All spark plugs removed... what are the actual psi compression numbers of the individual cylinders? Standing in back of the engine, facing the spark plugs, the cylinders are numbered as:

    Spark: Still with spark plugs removed, the spark should jump a 7/16" air gap on all cylinders with a strong blue lightning like flame... a real SNAP! Does it? Note that small single cylinder air gap testers are available at auto part stores.
    (Spark Tester - Home Made)
    (J. Reeves)

    You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

    A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

    Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:




    This can obviously be modified to a 6 or 8 cylinder setup tester.
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    • #3
      Thanks Joe, I will get back later with precise information. Finished cleaning the carbs today, they looked really clean from the last cleaning last year. Only reason I cleaned them was i wanted to make sure cly 2 is getting fuel as that is the spark plug that was dry. I will put the carbs back on tomorrow, install new spark plugs and see what happens. Will advise later. Thanks


      • #4
        Be sure to check the high speed jets... make sure they're absolutely clean pertaining to their ID.
        Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?


        • #5
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          I cleaned the carbs, which did not look dirty at all, and took the boat out to lake and did a test run today. It ran great, full power restored. Cleaning the carbs may have helped but I think changing the spark plug wires back to original , assemble yourself ends and boots, did more than anything to help. I took one of those store bought, machine assemble blue spark wires and cut it in half, looked like nylon threads, no real wire. I also change spark plugs. I only ran the motor for around 5 mins but it was running like a new motor. Had it up to 6000 rpm's for just a couple of seconds, but mostly ran it around 5200 rpm's. I sure hope when I go fishing for the day next week it will run like that the whole day. Then I will be happy and confident my problem has been solved after working on it for over a year trying to figure it out. Thanks for all the help here.