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1993 Johson 150 h.p. outboard silver star (carb)

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  • 1993 Johson 150 h.p. outboard silver star (carb)

    Hey folks!!

    I recently acquired a very good shape 1981 Mako with a 1993 Johnson 150 on the back. I got this boat knowing I was in for a project but also thought I was doing a good investment and nominal money to get it purring again.

    Motor worked ok during test when guy sold me boat. Boat would not idle properly. So you could manually press the the throttle lever and boy those older outboards sound awesome when they revving but wont hold idle.

    So I got new spark plugs, charged the batteries, changed the gas out and oil. And hoping for better effects. A friend of mine is a good motor guy but he mostly works on inboard motors. He is not as proficient on outboards.

    We did a check on the brand new plugs and the base of the plugs was wet like sloppy and the caRB holes were damp as well almost enough for a drip to come out. My buddy says this thing is running to rich. I spent 49 bucks on a motor manual on but do not see a section on how to adjust the motor that is running too rich. Forgive my explanation if its not that good. I am into fiberglass and cosmetic stuff but a green horn on motor work.

    Any and all feedback is welcome. Thanks for your time.

  • #2
    Youll need to check compression first and foremost. If compression checks out pull the carbs and rebuild/clean each one. I had a similar situation where motor would run but wouldnt idle, turned out I had low compression in 1 cylinder due to cylinder wall damage.
    Long Island NY [br]1985 Mako 20C[br]2003 Yamaha OX66 150[br]


    • #3
      Hey thanks for the response. We did a compression test my buddy did, when I bought the boat. He used the one that screws into the spark plug holes. For his knowledge it check out good. But all were not the same. Some were 97 some were 105 some were 110. Are these all supposed to register the exact same compression or is there a small wiggle room there? Maybe we need to do that again. and get a more accurate reading. The gauge we were using the needle was already advanced a small bit before plugging it into motor. hmmmmm.


      • #4
        The older John-rudes did not have high compression- The closer the PSI the better- you are pretty much at max acceptable range.

        Has the motor been sitting for sitting while? If so carbs are probably funky- I do not automatically buy gasket kits for carbs when I tear them down- lots of times they can be re-used unless you tear one. Do carbs for sure, set link and sinc. Checking timing.

        One often over looked thing on timing is to hold butterflys on carbs wide open- this allow max air flow-

        If you want go do a real check of block condition- do a leak down test- google it- tool is about $70-80 and you need access to a decent little air compressor- Not a tire pumper-

        I will bet on dirty carbs.... use Chemtool B12- it will melt stuff that treats store brand carb cleaner like water-


        • #5
          I meant to say hold carbs open when checking compression- not timing-


          • #6
            Yeah, clean the carbs by taking them apart (not just running a "cleaner" through the gas), and report back.
            ROGUE I[br]1978 235 CC[br]Newburyport, MA[br]ROGUE II[br]1987 17\' Montauk[br]Camden, ME[br]


            • #7
              Awesome awesome feedback here. Great feedback. Had buddy come over. Took carbs off one by one. There was a thick jelatin like jello solution in the buckets of each carb under the floats. nasty. quick trip to auto parts store. Couple cans of carb cleaner. and presto. gaskets looked ehhh 50/50. We put her back to gether. And presto. She idles. Wow. She idles. Awesome. However putting her into gear she chokes out. So floats old? out of adjustment? carb gaskets leaky?

              Ordered carb kits new. About 16 bucks per kit including floats.... and ordered six of them. We will do it again. With new gaskets this time and new floats. Great help from this group I appreciate. And now I can say I have taken apart my carbs on my boat motor. Pretty cool to be able to say that.

              Will update after new carb kits are in. Thanks for all the feedback....


              • #8
                You have to use a small wire and clean out all the jets -- the idle jets are very tiny...
                ROGUE I[br]1978 235 CC[br]Newburyport, MA[br]ROGUE II[br]1987 17\' Montauk[br]Camden, ME[br]


                • #9
                  To add to the carb cleaning. I have a pair of 1993 175 HP Evinrudes. Basically same engine. Idle & low speed mixture is controlled by those tiny jets. The aluminum intake manifold, thats the part with the butterfly valves, is really the idle/low speed part of the carb. There are (2) sets of tiny (3) holes mixture jets. On those engines you need to pry out the port covers (2 per carb/non reusable) and clean those passageways. I actually use micro drills and WD-40 to ream them out. And I have 12 carbs to do!!
                  Gloucester, MA[br]1973 20C with 175 Evinrude[br]1993 233 with 2X 175 Evinrude