Outboard help?



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  • Outboard help?

    Wondering if any of you have experience with a small outboard that lacks some power at the top end.

    If I choke it a tiny bit (not to the first detent) it picks up and seems to run as it should...push the choke back to normal run position and it picks up a tiny bit more before quickly bogging back down. Runs fine there, but just lacks that extra little bit of the power band.

    I cleaned the carb - no varnishing or anything ugly. The main jet is a fixed size, not adjustable. Adjustment screw for idle mixture. Replaced fuel pump diaphragm and cleaned filter screen. Fuel hose/bulb is new. Points have been cleaned and adjusted.

    I assume that it's running lean (by reducing airflow with the choke it runs better - too little fuel or too much air??)

    If that's got everyone stumped does anyone know a superb old outboard doctor (old is referring to the motor not the doctor!) that could fix it up?

    Thanks in advance.

  • #2
    You did not mention the manufacturer or model of your outboard. If it is an old Eska like many up here it is generally the fuel pump. Remove the carb and there is a small diaphram between the carb abd block. A pin hole will cause lean at high speeds, a big hole will cause it to not rev at all. There are many Tucumseh powered outboards that have this set-up. They were branded by Sears, Montgomery Wards, and others.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
    Bill Hicks


    • #3
      oops -
      she's an old (20 or so years) US Marine Force 15 hp - already replaced the fuel pump diapragm (no visible problems with the old one, but it's new now)


      • #4
        Hey, this sounds like my problem .. .. ..

        I also have an old (1980's) 30 hp Mariner that is also lacking in top end power.

        She starts right up, runs just fine until you give her about half power. After opening the throttle up, she runs the same as when she was at the half power mark.

        Ideas on this one?

        -- Gambler


        • #5
          have you checked the compression? I did on mine and got about 100psi per hole - no drastic difference between the two and although I can't find the spec, most similar engines seem to be about the 115-125 range. So although mine is a bit low I don't think it's horrible - also the correction of the problem with a little choke leads me to believe it's not a compression problem in my case.

          A leakdown test is another good one to do, but I don't have the gear for that one - if I can find rings for it I may just plan to re-ring it over the winter...couldn't hurt


          • #6
            wow...what a dud of a thread that was...all I found was another poor sap with a curmmy outboard! Not even an repair shop recommendation in the interior?

            I guess I better go back to my plan of adding additional thrust with bottle rockets! Or maybe a gross of those old baking powder submarines?


            • #7
              Advice on the internet is worth exactly what you pay for it, and typically the more specific you are in your question, the better the replies will be.

              If your engine runs better with the choke on, it sounds as if the engine is running too lean with the choke off, ie not getting enough fuel. There are a few things that can cause this. A bad fuel pump can cause this. Cracked fuel lines can cause this. An air leak in the crankcase can cause this, two stroke engines required a sealed crankcase to pump fuel/air and leaks will cause the engine to run lean. The gaskets on the crankcase and cylinder rarely fail, but crankshaft seals can dry out and crack with age.

              I'm in Southcentral so am of no help recomending and interior o/b wrench.
              Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

              If you have a tenuous grasp of reality, Alaska is not for you.


              • #8

                AKJ, call Reed's snowmachine and marine repair in Fairbanks and describe your symptoms, maybe he can help. He helped me with some O/B diagnosis I needed. If he does the repairs, he wont kill you with the price either. Maybe he'll take a few baking soda subs in leui of payment....lol!
                Proud to be an American!


                • #9
                  fullkurl - thanks for the Reeds tip - I'll see what help they might be. Glad you got a laugh! (people on the river sure look at you funny when your pouring baking powder into the gas tank!)

                  Paul - that was really just a bump with some humor...not meant to gripe. I've heard that a leak in the crancase (cylinder?) can cause problems and that it can sometimes not be detected with a compression test. Is this where the leakdown test comes in?

                  Is there a fuel conditioner or anything for 2 cycle engines to treat seals? Lots of crud like that for auto engines...

                  I guess I should see how expensive a rebuild kit is and just overhaul it in the off season.



                  • #10
                    Yes you need a leakdown test to check the crankcase. Unfortunately a fuel conditioner won't fix bad seals, they'll have to be replaced. They're relatively inexpsensive parts, but alot of labor to get to them.
                    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

                    If you have a tenuous grasp of reality, Alaska is not for you.


                    • #11
                      How did you clean the carb? Did you tear it down& soak it?


                      • #12
                        AIr leak or still something in the main jet

                        If it runs better choked that means that it's obvously lean. Choking however does not only limit the air flow as it also puts engine vacuum on the main jet which pulls significantly more fuel then venturi vacuum alone. If your certain that the jet is clean, run it in a tank and start spraying the outside of the carb, carb attach point, and engine crankcase with a spray bottle of water (on stream), the engine will change pitch enough to hear it and you will usually be able to pinpoint the leak this way. I usually use a can of carb cleaner for this, as it not only subdues the leak for a second but the engine will increase RPM as you are adding fuel, and the spray nozzle is very precise. If you go this route, be very careful not to hit areas around spark plugs and coils, as if you have an ignition lead that is going bad you WILL have a fire. Also, keep an extinguisher handy. If you spray around all the seals and possible air leaks and come up empty you will need to contact an outboard dealer and see if there is a different size of jet for this engine as the engine may have come from high altitude. (I don't know it's history)

                        Hope this helps,


                        • #13
                          redr, yep exactly that - also ran it while spraying some carb cleaner

                          Chris - interesting - thanks for the more detialed info on the choke.

                          I still need to pull the carb off again and get the jet size - found a chart online showing various jet sizes for it and their associated altitude range. I'll be surprised if the jet in there is not the 0-2500' unit...as the engine was new in AK and never left.

                          The engine had sat for years before I got it.

                          Can I poke a small wire through the jet and other carb passages to maybe knock a chunk loose if there is some kind of blockage?

                          Guess I have a few things to do and try -
                          • pull the carb
                          • clean the jet (don't forget to note the jet size and write down carb numbers in case I have to buy parts!)
                          • spray test for leaks
                          • hope that I can finally catch a break with this tub!
                          Thanks for the help!


                          • #14
                            lots of good advice here...

                            looks like the motorheads came around.
                            One more tip, AKJ, and you probably know this, but never put forced air into the fuel line at the carb to "clear" it out. Its an easy way to screw up a diaphram and floats etc...
                            Best of Luck, Frank
                            Proud to be an American!


                            • #15
                              yikes...never thought of that, but yeah...sounds like a bad idea! Thanks for the preemptive strike on stupidity!

                              Someone else told me to check reeds in the intake? I'm no engine dummy, but have never dealt with reeds before - is this a complex inspection or just an easy visual thing like spark plugs? Is there an adjustment to them? I don't have gaskets - is the intake gasket likely a remove and replace unit or re-installable?

                              Guess if I have to pull the carb again maybe I should pull the intake, but if I have to order gaskets I'll wait till the rain starts again!


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