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1996 225 Power Loss

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  • 1996 225 Power Loss

    1996 Salt Water Series
    Model: S225TXRU
    V-x Yamaha Engine
    Engine Type: 76 Degree V-6
    Displacement: 3130cc
    Micro Computer Ignition
    Naturally Aspirated; Carbureted

    Please provide cylinder number/orientation and firing order.
    Help with Problem Diagnosis and Solutions.

    Problem followed by Tests Performed

    Viewed from back of PowerHead, Top PortSide Cylinder Fails to produce Power.
    Observations: Engine, at 2,800rpm is missing Considerably. On the water, WOT yields merely 4,200rpm; rpm decreases some & power weakens with time at WOT. See SparkPlug whaler1990 Album picture. Note the plug on the right. It is from the Top PortSide Cylinder and after one-hour running it appears new; no carbon discoloration. All plugs were replaced a forehand and at time of the picture, all had about one-hour runtime.

    Therefore the focus of test is primarily the Top PortSide Cylinder.

    All testing performed using Premium Ethanol free fuel in a new dedicated five gallon fuel tank.

    Check Coil KV@2,800rpm
    Procedure/Observation: Take KV readings from SparkPlug wire, just before spark plug.
    Disposition: Problem cylinder is high on both of two separately installed coils. Viewed from back of PowerHead:
    💥16KV 5KV
    6KV 6KV
    7KV 7KV

    BoreScope Top PortSide Cylinder Wall
    Procedure/Observation: Bore scope inside of cylinder and note observations.
    Observation: Cylinder Walls appear normal through the BoreScope; walls are wet and machining cross-hatching remains visible.
    Cylinder Top appears normal; carbon color with casting surface perceptible.

    Secondary Compression
    Procedure/Observation: Check secondary compression & note readings; viewed from back of Powerhead
    Run test Cold
    100psi 95psi
    95psi 93psi
    90psi 89psi-90psi

    Check Valve
    Procedure/Remedy: Apply 11.6psi/replace if BackFlow is noted.
    Manual Pg 4-2
    Disposition: Pressure holds at 11.6psi

    Initial Fuel Flow
    Procedure/Observation: Pull fuel line from Carburetor, remove SparkPlug Wires, Turn engine over & record fuel flow.
    Disposition: Fuel discharged much Fuel. Squirts in HARD Pulses.

    Check Fuel Pump Pressures
    Procedure/Observation: Isolate each of the three Fuel Pumps; perform three individual checks. Disconnect outflow hose (the one coming from the fuel pump) from the carburetor. Connect a pressure gauge to fuel pump outflow port. Run engine & observe fuel pressure at each pump.
    Top Pump About 3.0psi
    Middle Pump 4.0psi
    Bottom Pump 4.0 to 5.0psi

    FuelPump (1) Diaphragm
    Procedure/Remedy: Apply vacuum to out port & block input port. Replace if vacuum LeaksDown
    Manual Pg 4-2
    Disposition: No remarkable LeakDown; tested dry.

    🚫FuelPump (2) Test A
    OutLet Valve
    Procedure/Remedy: Apply 7.2psi positive pressure on outlet port; leave inlet open. Replace if BackFlow is noted.
    Disposition: Unable to pressurize due to lack of pressuring device w/gauge. Will advise when completed.
    Manual Pg 4-2

    FuelPump (2) Test B
    InLet Valve
    Procedure/Remedy: Apply 4.3psi vacuum on inlet port; leave outlet open. Replace if BackFlow is noted.
    Manual Pg 4-2
    Disposition: Holds vacuum in dry condition with slight backflow, may be apparatus tubing leak.

    Electric Fuel Pressure Pump Discharge & Pressure
    Procedure/Remedy: Capture five seconds fuel discharge from Electric Fuel Pressure Pump. Min 41cc must discharge over a period of five seconds with Key-on. Check fuel pressure
    Manual Pg 4-6
    Disposition: 58CC in Beaker over 5 seconds at 4.0psi

    🚫Fuel Pressure Regulator
    Procedure/Remedy: Apply pressure to pressure regulator. Regulates Pressure at 1.4psi
    Manual Pg 4-6
    Disposition: Manual is unclear exactly how to test. Will advise when completed.

    Enrichment Line Filter
    Procedure/Remedy: Remove enrichment line & blow out filter from inside Fuel Control Port.
    Manual Pg 4-9
    Disposition: Bore scoped the enrichment port and the enrichment line filter tube; no debris or buildup observed. Lightly applied air from inside the enrichment valve hole being careful to not lose the O-Ring; some fuel and no apparent debris or dirt exited the filter tube.

    Pilot Screw
    Procedure/Remedy: Remove & Inspect. ReInstall until seats softly; turn out 1 1/8 Turn +-1/4. Replace if taper is worn.
    Manual Pg 4-9
    Disposition: No apparent wear on pilot screw taper is noted. Original machining is in tact and undisturbed.

    Test Fuel Control Solenoid
    Check Valve Closes/Seals
    Procedure/Remedy: Apply 1.4psi pressure & it should hold for One-Minute. If Leak-down Replace.
    Manual Pg 8-18
    Disposition: Leak-down test acceptable; holds much longer than one minute.

    Fuel Control Valve Opens
    Procedure/Remedy: Apply 1.4psi pressure & it should hold thence release when 12volts are applied to solenoid
    Manual Pg 8-18
    Disposition: Pressure release test good

    Check Fuel Control Solenoid (Enrichment Valve) at Carb while Engine Running
    Procedure/Observation: Disconnect Fuel Control Solenoid from wiring harness. Run rpm up until engine is missing; hold that rpm. Thence apply 12 volts to Fuel Control Solenoid.
    Observation: Engine rpm drops but, engine smooths out; miss substantially subsides.

    Test Firing by Pulling Plug Wire
    Procedure/Observation: Note rpm difference with SparkPlug wire connected/disconnected.
    Observation: No rpm difference noted with SparkPlug wire connected or disconnected. With other cylinders, idle rpm substantially lowers when SparkPlug wire is disconnected.

    Test Firing by squirting fuel into Carburetor Venturi during high speed miss
    Procedure/Observation: Inject fuel into carburetor Venturi during the high speed miss.
    Observation: Shortly after injecting fuel into carburetor, the high speed miss desists momentarily thence begins again.
    Attached Files

  • #2
    clean the carbs.
    at 16Kv it is running lean.
    lean mix takes more to fire.
    also check the spark plug cap resistance.
    open resistor = more Kv needed to arc.
    a normal running 3.1L usually fires in the 5-8Kv range.
    but if you can squirt fuel in the carb and it picks up, that carb is not flowing fuel.


    • #3
      Carburetor is headed for a Berrymans bath.

      Cap resistance is 4.855 ohms on the 16Kv cylinder. In an effort to keep me referencing cylinder numbers correctly, what are the proper cylinder numbers for each of the cylinders as viewed from rear of the powerhead.

      Thank you for the expedient response.


      • #4
        we NEVER disscuss left and right while standing on the dock barking at the moon.

        the bow is the pointy end.
        the stern is the square end.
        when standing at the helm looking at the bow the starboard side is to the right and the port side is to the left.

        \port side cyl top to bottom is 2 4 and 6.
        stbd side top to bottom is 1 3 and 5.

        you would not belive how many issues we have with customers using left and right instead of port and starboard.


        • #5
          1996 225 Power Loss

          Right on target Rodbolt; cleaning the #2 carburetor smoothed things up remarkably. I suspect that I should continue through the remaining five carburetors. I've not decided whether good luck or bad but not moments after startup I smelled electrical heat/burn.

          Smoke billowed from under the rectifier cover. Shut it down, hit the battery disconnect, and pulled the cover for a better view. Smoke subsided but could not feel heat; it's water cooled. New rectifier ordered.

          Two Questions; I do not want to ruin a new rectifier--to my knowledge, this rectifier/regulator is the original 1996 part. Is there some common reason it failed so dramatically or just age and sitting through too many -30 degree winters? Finally, along with the new rectifier, what else should I test or replace before installation?
          Attached Files


          • #6
            check all battery cable connections.
            use a voltage drop test on the cable connections.

            NEVER run that motor without a tell tale.
            no tell tale no rectifier cooling.