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newbie to four stroke outboards, need help

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  • newbie to four stroke outboards, need help

    Ok, well this is my first time to play around with a small four stroke outboard. I've had plenty of experience working on snowmobile motors and some two stroke outboard motor exposure.

    I have quite a few questions to kick off my motor testing and repairs (if needed).

    1) Does a two stroke gas tank line fitting fit on a four stroke
    2) Are the gas line fittings brand specific
    3) Where can I find the model on the motor, all I see now is it's a 9.9hp
    4) What should be examined before I even attempt to start it.
    5) How can I determine the battery cable polarity hook-ups

    I'd really appreciate any help the forum members might be able to give me on getting this motor up and running. Who knows it might not need much. The motor doesn't seem very "old"

  • #2
    Tank fittings are same as 2 strokes, just get Yamaha fitting for your model year motor.
    Model and serial number is on side of transom bracket.
    Check engine oil level, gas to carbs and put in water or connect flusher before starting.
    Red sleeve on battery cable is positive, black is negative.
    Yamaha Outboard Parts


    • #3
      Thanks for all of the info. If I do get it running, should I worry more about the lower unit, shaft seals, and water pump first instead of making sure it runs 100% perfect. I assume the motor may need some tuning after it's put under load and not just sitting in a coolant tank.


      • #4
        cooling is absolutly critical on an outboard.
        takes priority over everything else.
        do a leakdown test on the cylinders.
        clear the fuel system.
        replace the water pump.
        run it.


        • #5
          finally got a chance to look at the model plate, it's a T 9.9 exhp First thing I noticed right off the top was a vacuum tube that is not hooked up on the carb. When I look up the carb parts break down for a 91 it shows two lines, #16, but on the motor I can only seem to find one place it would fit on a barb. does one get blocked off after tuning or something? I've got to download a manual for this thing for sure.


          • #6
            There is one hose that doesn't connect to anything.
            Yamaha Outboard Parts


            • #7
              Well it's been forever since I've had a chance to play with this thing. Carb was plugged up but not terrible. I clean everything in the carb real good. I have the opportunity to use our sonic cleaner at work and used it to help clean all the super tiny passages in the carb. It is spotless now. I have a new fuel filter put inline.

              Got some new gas, my tank hooked up and pulled it over using a crod wrapped around the flywheel (no battery right now). It only runs for about as long as you can read this, bbbbbrrrrrrrrruuuuuuuuuuuuuummmm da bum bum. After that it stalls. Fuel pump maybe? Air screw setting right now I have it at 1 1/2 turns out from seated.

              The crazy part is, I had it running for about a minute with the carb not even cleaned and a little shot of carb cleaner in the carb. Only one shot, I didn't keep feeding the motor carb cleaner to keep it running. This is what makes me think the fuel pump could be an issue.


              • #8
                carb is clogged,still.
                even a NO fuel pump it will run several minutes on the fuel in the bowl.


                • #9
                  Well, I disconnected the fuel line from the pump and pulled it over. It fired right up and ran fine. I put the fuel line back on the pump and it died shortly after that. So here's what I'm guessing might be part of my problem. The fuel pump is pushing fuel past the seat and causing the motor to be flooded and stalled. Sound reasonable considering it ran without the pump connected??

                  I'll have to take the carb off and check the seat. It's the only thing I didn't check in the first place because I didn't press the pin out that holds the float in place. I don't think that the carb is plugged, I ran a fine wire down all of the passages before sonic cleaning it and blowing it off with high pressure air. The carb looks spotless.

                  I've got to check the spec on the air screw turns and see if I can set the butterfly height exact. I didn't touch the screw that adjust the butterfly, that's the idle screw on these carbs right?

                  Thanks again for all the help so far.


                  • #10
                    The tip on the needle looks ok until you push on it a bit then a crack shows up on the tip. I'm going to replace it and see if that does anything to help keep it running. any kind of safety stops on a little 9.9 like this one.

                    Oil pressure sender being bad may be causing it to shut itself down??

                    just bouncing ideas of the people who know their $hit. Again, thanks for the advice so far.


                    • #11
                      no shut off features.
                      it does have an RPM reduction feature for low oil pressure,some models also have RPM reduction for overheat.


                      • #12
                        Is there a way to fool the oil pressure sender to check if that is the problem. Disconnect leads and short them together?


                        • #13
                          You seem to be jumping from one possibility to another, concentrate on what you are doing, one thing at a time, do the carb PROPERLY and go from there, dont get side tracked trying to short things out.


                          • #14
                            Yeah, true. carb is all cleaned again but I've got a new needle coming for it. I've read through a downloaded manual quite a bit but I can't seem to find what a BVS valve is ( I hate acromyns) and if that can effect the carb substantially. Seems like a simple carb so I keep jumping to something else as the problem on this motor.


                            • #15
                              Well, I cleaned the carb one more time and assembled it. Changed the oil. The very last drops of oil had a slightly chunky look to it. Flushed out the oil filter that was all gunked up.

                              New oil and fired it up. Runs just like before. Arrrrgh If I crack the throttle is will rev up a bit then hesitate a bit, cough and die. at least once or twice, I thought I heard a back fire through the carb before it died. It seems to smoke more than I would think that a 4 stroke should too.

                              I may flush out the gas tank I have. The one I have may have too much varnish getting washed off the inside of the tank by the new gas and tha's not letting it run right. I know that is a long shot. It doesn't seem like that could keep it from running right.

                              Air screw set to 3 turns out per the manual. Is this right? Most other carbs I've dealt with were 1 1/2 turns out on the air screw
                              Timing?? is there a chance that the timing could be off a bit.