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Johnson 4hp (1969) tune up (high and low speed)

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  • Johnson 4hp (1969) tune up (high and low speed)


    I recently got an old Johnson 4HP engine (model :4R69R)

    It didn't start so I cleaned out the carb and replaced the ignition parts (coils, points, spark wires etc)
    Now it starts and runs fine but I have no clue how to 'tune' the high and slow speed needle.

    Does someone have some tips for this ?


    PS : we want to use the engine for our recently bought Corsaire trailer sailer

    Click image for larger version

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  • #2
    Re: Johnson 4hp (1969) tune up (high and low speed)


    Follow this link:


    This link and other helpful links are found under the "Top Secret Files" stickies...the first thread on this forum.

    "New" '57 Lark Chapter One...the Find:

    "New" '57 Lark Chapter Two...the Initial Breakdown:

    "New" '57 Lark Chapter Three...the Gearcase:

    "New" '57 Lark Chapter Four...the NOS Powerhead:

    "New" '57 Lark Chapter Five...Repainting:


    • #3
      Re: Johnson 4hp (1969) tune up (high and low speed)

      HI iGrif. Welcome to iboats. The link above is great. Be sure you run the motor in a test tank with water filled up to about and inch or two below the main exhaust port while dialing in the idle. These older models can't run on muffs. Also be sure that you tweek the settings once you've actually got the motor on the water. Setting the lo speed idle in the test tank will get you close, but most tanks don't offer the same exhaust back pressure that the open water can, and you need to reach WOT under laod to set the hi speed needle properly anyway. While trying to dial in the idle, snug down the brass nuts that the hi/lo needles pass through into the carb such that you can still adjust the needles as needed, but not so loose that the needles can back themselves out due to the vibrations of the motor. Once the needles are set, tighten down the brass nuts the rest of the way and you shouldn't have to fiddle with them again. Here are some other handy links. Good luck.



      • #4
        Re: Johnson 4hp (1969) tune up (high and low speed)

        thanks for the replies, lot's of useful info behind the links you both provided !

        I have the engine in a big watertank so that's covered, as long as I can get it to run more or less ok then I can do the final adjustments next time we're on the water !

        good tip about the brass nuts though, I didn't realize they were used to 'lock' the needles in place.


        • #5
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          Re: Johnson 4hp (1969) tune up (high and low speed)

          I wouldn't tighten them to the point the needle is locked. At the very least I'd wait until you have a few trips on the motor. They only need to be snug enough that they don't vibrate out of adjustment. Best of luck. Rick.