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1989 Yamaha 9.9 four stroke

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  • 1989 Yamaha 9.9 four stroke

    Hi guys,

    After many an hour searching this and various other forums on this topic here is my first post.

    After perfect service a few weeks ago by OB was hesitant cold starting almost like it wasn't automatically choking. This is the model with vacuum operated choke so I managed to get the casing off and manually choke the engine. However things were still not right....I managed to make it back to dock with a high tickover setting etc.

    So the next day it starts fine on its own autochoke but as soon as the choke goes off it bogs out, when trying to rev up it bogs and is generally happy to the point if held at higher throttle positions it will just bog down and stall. It was screaming fuel starvation/fuel issues. The priming bulb didn't feel quite right but I think this was more in my head the easy fix?

    So bought a new tank (wanted a larger one anyway) complete with new supply line and priming bulb filled with fresh new fuel and filter. No change. Has to be the carb....pulled this off and stripped down. Was upset to find nothing of any consequence - wanted to find something gunked up etc.

    Stripped everything, found the hidden pilot jet which were all clean but used cleaner and compressed air to blow through any orifice I could find. re fitted and still the a few forum posts ref HT coils and Cdi breaking down when warm and under load so have swapped these out for known good spares no improvement.

    I've installed the main jet holder as per the Clymer manual i.e. the cutaway facing toward the engine but have read a post today suggesting this is incorrect - can anyone confirm?

    Can anyone give any more advice on choke and how all the vacuum pipes work - all look good but trying to get an insight into what does what etc. The choke diaphragm is good I've operated with manual vacuum and it runs good when cold perhaps a little lumpy but its on choke right? The Clymer manual suggest the small brass thing on the carby is the vacuum choke valve but I believed it was the unit bolted to the block that controlled choke so what do the other two smaller hoses do? Is choke on when plunger is up or down? Should the vacuum valve open when warm or close etc? I want to ensure the hoses are doing what they should when they should.

    Any help, advice or similar experiences greatly appreciated - don't know what else to do now. Other than look for a new OB

    Thanks everyone

  • #2
    Can you post your model # please?

    This is one model of a 9.9, 1989 4 stroke:
    1989 F9.9LF Yamaha Outboard CARBURETOR Diagram and Parts

    Did you pull the jets completely OUT and visually check that all orifices are clear?

    As for the main jet, not sure what holder your referring to but that jet should be snug.

    And please clarify " perfect service a few weeks ago by OB "... Did someone do a full maintenance on the engine, touch the carb at all and what's "OB"?

    And lastly, after the service work, is that when the problems started or was there an issue BEFORE?

    ***Once the engines warm, it doesn't need the choke at all. If its still bogging, not revving, etc, it sounds as if there's still crap in the carb...
    Last edited by TownsendsFJR1300; 06-18-2016, 04:33 PM.
    1997 Angler 204 CC, 2006 F150 TXR


    • #3

      thanks for your reply.

      In response:
      It is (I'm told) an F9.9B.

      Yes I pulled the jets completely out, even found the one under the nylon plug which was clear although a very tiny hole.

      The main jet holder - the climber manual calls a holder slides into the venturi and is held by a small screw and can be installed incorrectly by 180 degrees as it has a cut out and the manual says to install cut out toward engine but have seen a forum post saying should be installed away from inlet manifold.

      On the last point - typo on my part I'm afraid - I meant to write the OB has been putting in perfect service, working fine UNTIL a few weeks ago. Working perfectly when I tied up, the next morning the trouble was there. There has been no issues since, it had a service late last year with many hours trouble free since.

      I'm going to strip the carb again tomorrow in case theres something I could have missed.



      • #4
        No problem Dave.

        I'm not familiar with that "holder" you reference to but would probably go the way the manual states. NOT everything on the net is true...

        Your model isn't listed here(not un-common from outside the US)..

        Is your fuel pump like this one here:

        if you can, when the engines not running right, stop and pull the spark plugs. Check to see if one or all are dry or excessively wet with fuel..
        Last edited by TownsendsFJR1300; 06-18-2016, 07:28 PM.
        1997 Angler 204 CC, 2006 F150 TXR


        • #5

          Yep the pump looks just like that, I've had this off and pumped manually with by hand, it should run on a full float bowl for a while anyway. The carb also is exactly like the one on the link in your previous post.

          Both plugs are quite dry, one is dirtier than the other, only slightly they are new plugs that have run for maybe thirty minutes - one of the first things changed.


          • #6
            Maybe Rodbolt or someone else that is familiar with that type of 4 stroke carb will chime in on how that choke system is suppose to function.
            I have no clue


            • #7
              When it starts to bog - try squeezing the primer bulb. If that improves the situation - it's an issue delivering fuel to the carb. If it doesn't improve, it's likely within the carb system.


              • #8
                Cheers for responses so far.

                I had tried squeezing the bulb and it stays lovely and hard throughout and haven't actually managed to squeeze any additional fuel in there assuming that's the symptom when the float bowl is full....?

                I'm thinking the enrichment/choke plunge is up for choke on and down for choke off? It seems to even out the running when it's almost warmed up when I lock the plunger down - just trying to ascertain which way is on/off etc so I can determine if richening improves it or if I am weakening the mixture if that makes sense so I can follow the symptoms out.

                Awful weather today not managed to get to the marina and remove the carb again.....will post up how it goes if I get up there after work tomorrow....



                • #9
                  Had another minor light bulb moment...

                  How does the oil pressure warning work? I see it is coupled to the CDi does it work to cut out the spark on a cylinder or similar ? Although the coil looks like it's a waster spark set up I.e both plugs spark together. A few days ago when it would bog down if I stopped the engine and started it again it would Rev out almost like normal for about five seconds or so but quite consistently every time I switched it off and ran her again. Just wondered if a fault in the pressure switch or wiring would have an effect it operates the warning light ok on the controls but never know....?


                  • #10

                    Bit of a bump...but also.

                    I haven't suspected anything relating to over heating etc as the engine block doesn't seem too warm at all. However should I be getting water out of the hole below the power head in the leg, the one hole which isn't a huge amount above water line? The tell tale is good and strong but just wanted to cover bases.

                    Still no luck with the carb - just as bad as it was before - considering a new OB for hopefully fit and forget reasons.