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Mercury Classic 50 Bogging down - No Power - Carbs Rebuilt - Test Results in Thread

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  • Mercury Classic 50 Bogging down - No Power - Carbs Rebuilt - Test Results in Thread

    Mercury Classic 50 (45HP 2-Stroke Outboard)
    S/N: A949635
    Symptom: Bogs down under any load, will not plane boat


    Good evening,

    I am currently helping a buddy work on his Mercury Classic 50 outboard. A little over a month ago, he called me from the lake stating he had fuel gushing out of the front of his upper carburetor and it would not stay running. His outboard uses the carburetors with one separate external fuel pump instead of the individual fuel pumps. The following correction actions were taken:
    • Disassembled Carburetors & Allowed To Soak in Carburetor Cleaner Dip
    • Used Compressed Air to blow out all passages after soaking carburetors
    • Visually inspected all jets to verify no blockages
    • Replaced & set floats in both carburetors
    • Reassembled Carburetors using new mercury OEM gasket set
    • Tested float for proper function
    • Installed carburetors
    • Rebuilt external fuel pump using new Mercury OEM diaphragm kit
    • Replaced all fuel lines from Carburetor to fuel pump, to engine fuel connector
    • Replaced fuel lines from tank to outboard

    However, after getting everything properly connected, the outboard still seems to lack power and bogs down quickly when the throttle is increased. Sometimes you can keep it running by pulling back on the throttle, but usually it dies out. I have adjusted both carburetor mix screws 1/2 turn at a time trying to find a sweet spot, but to no avail.

    This began to remind me of the time I sucked a twig into the throat of one of the carbs on my 200 Black Max outboard and chased what I believed to be a fuel problem until later finding out I had blown a switch box at the same time. So, having a few moments today, I performed tests on the outboard with the following results:

    Compression:
    • Cyl 1: 130lbs
    • Cyl 2: 132lbs
    • Cyl 3: 130lbs
    • Cyl 4: 126lbs

    Spark Test: All four cylinders were capable of jumping a spark tester set to 7/16" at cranking speed with a fully-charged starting battery.

    Stator:
    • Blue ~ Blu/Whi - Resistance Within Spec / DVA Measured Within Spec
    • Red ~ Red/Whi - Resistance Within Spec / DVA Measured Within Spec


    Trigger:
    • Purple ~ White: Resistance & DVA Within Spec
    • Brown ~ Whi/Blk: Resistance & DVA Within Spec
    • Purple ~ Engine GND: Resistance when disconnected within spec (Open) Shows ~19k ohms when connected to switch box - DVA Within Spec
    • White ~ Engine GND: Resistance when disconnected within spec (Open) Shows ~19k ohms when connected to switch box - DVA Within Spec
    • Brown ~ Engine GND: Resistance when disconnected within spec (Open) Shows ~19k ohms when connected to switch box - DVA Within Spec
    • White/Black ~ Engine GND: Resistance when disconnected within spec (Open) Shows ~19k ohms when connected to switch box - DVA Within Spec

    Coils:
    1. Primary / Secondary Resistance Within Spec
    2. Primary / Secondary Resistance Within Spec
    3. Primary / Secondary Resistance Within Spec
    4. Primary / Secondary Resistance Within Spec

    Now... the only thing I haven't done that I could see as being prudent would be to empty the fuel in his fuel tank and replace it with new fuel. However, the fuel in the tank is not very old (Maybe 2 weeks) and was treated with Star Tron as soon as it was pumped into the tank. The carburetors are completely clean and no amount of adjustment of the mix screw allows the outboard to run correctly.

    Since I'm seeing an improper resistance from the trigger leads when connected to the switch box, I'm inclined to suspect a failing switch box. This boat doesn't have a tachometer, but when I had it on the water this past Saturday, it didn't sound like it was getting to the correct RPM. It sounded as though it was getting somewhere in the neighborhood of 3500RPM. Much like my 200 did when it was having similar issues.

    I'd appreciate any input from some of the Mercury gurus here. I've always had good luck in these forums, and am hoping that luck holds out.

    Thanks.

    "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
    Koos Brandt

  • #2
    Additional Information: Timing was checked when carburetors were reinstalled and the link and sync procedure was performed in accordance with the OEM Mercury Shop Manual which I own for this motor. Primary Throttle Pickup and Secondary Throttle Pickup is at the specified marks when measured at cranking speed.
    "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
    Koos Brandt

    Comment


    • #3
      Gushing gas from either the carb throat, and/or bowl vent is an indication of a Stuck Float, Dirt in the inlet valve, Damaged inlet valve.
      When you say "Disassembled Carburetors", did that include the Welsh type plugs being removed? a Lot of crap can remain in those areas, and will gum up the idle feeds when put back into service.

      You have reasonable Compression, you have good spark, unless you blotched the link and sync. You didn't mess with max Timing?
      Have you done a Cylinder Drop Test? Disconnecting a plug wire to see how much worse the engine runs. If no difference than that cylinder isn't doing its share.

      Initial mixture screw setting is 1 1/2 out from lightly seated. This setting is almost 99.99% of the time Too Rich, and leaner runs much better.
      Are the carbs tightened down properly? are they synced to each other and fully closed prior to the First Pickup setting?

      Comment


      • #4
        Check for exhaust blockage in the midsection.

        Comment


        • #5
          Originally posted by jimmbo View Post
          Gushing gas from either the carb throat, and/or bowl vent is an indication of a Stuck Float, Dirt in the inlet valve, Damaged inlet valve.
          When you say "Disassembled Carburetors", did that include the Welsh type plugs being removed? a Lot of crap can remain in those areas, and will gum up the idle feeds when put back into service.

          You have reasonable Compression, you have good spark, unless you blotched the link and sync. You didn't mess with max Timing?
          Have you done a Cylinder Drop Test? Disconnecting a plug wire to see how much worse the engine runs. If no difference than that cylinder isn't doing its share.

          Initial mixture screw setting is 1 1/2 out from lightly seated. This setting is almost 99.99% of the time Too Rich, and leaner runs much better.
          Are the carbs tightened down properly? are they synced to each other and fully closed prior to the First Pickup setting?
          Carburetor was COMPLETELY disassembled including removal of the Welsh plugs. I didn't mess with max timing. In fact, everything was dialed in when I installed the carburetors. I just had to set the throttle butterflies to open as they should. Carburetors are closed prior to first pickup and synced together. When testing the outboard on the water, I've ran everything from 1/4 turn open to 3 turns open on the carburetors. Best running condition was around 1.25 turns open per carb.

          I have not performed a cylinder drop test, but I will do so tomorrow.

          My thoughts here, drawing from prior experience, is that the switch box is not kicking in to the high side when the throttle advances past the switching point.
          "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
          Koos Brandt

          Comment


          • #6
            How well was it running before the carb flooded?

            Comment


            • #7
              Originally posted by jimmbo View Post
              How well was it running before the carb flooded?
              It's not my boat, so my time in it is limited, but it's been my feeling that it has lacked top end RPM ever since he purchased it. It takes a horribly long time to get on plane and only runs around 25mph when it finally does get on plane. He has to keep the motor in the full down position (It does not have power trim) otherwise the boat just runs around with its nose in the air. It just seems like a 16 foot aluminum boat should run faster than that. (I had a 1436 jon boat on which I put a 25hp johnson and was getting 30mph top end) The boat doesn't have a tachometer, and the yellow charging wires coming off of the stator were broken, so it wouldn't be possible to wire a tachometer in the standard way. I'm judging everything by the sound of the motor any time I've observed it.

              I tried swapping switch boxes yesterday, but unfortunately the one I had here that came from a donor motor has no fire on cylinder #3. Not exactly a bad thing since I was able to throw the defective box into the garbage so it doesn't get mixed in with good parts.

              I'm tempted to dump his fuel on my burn pile and then put fresh fuel into the tank just in case he's gotten some bad gasoline. That would definitely be cheaper than throwing a switch box at the problem.

              Now, one other thing I noticed today (I'm trying to pay attention to any detail even if it seems insignificant) is that one of the spark plugs had some deposits near the electrode that looked kinda like rust. The plugs are fairly new (Replaced April of this year) and he hasn't run the boat much at all since we usually use mine. If that cylinder block cover gasket has failed and is allowing water to enter a cylinder, it would most definitely cause a poor running condition. In fact, I saw in a review of the gasket at one of the vendor sites where a guy specifically mentioned that his mercury classic 50 was bogging down when put into gear. Again a $14 gasket is cheaper than a switch box.

              Just trying to follow the trail of bread crumbs here.

              "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
              Koos Brandt

              Comment


              • #8
                If the electrode has rust on it, there is a chance that water is entering the cylinder via the Exhaust Port due to a warped/cracked exhaust divider, and/or failed gasket.
                Since it has always been a sluggish engine, I don't suspect the gasoline being bad, but are the Strainers, in the tank and in the fuel line(or pump) clear?

                Any idea what prop he is running, and what RPM is the engine getting at WOT?

                Comment


                • #9
                  A failed head cover gasket can not allow water into the cylinder.------The block does not have a cylinder head or a gasketed joint.

                  Comment


                  • #10
                    I’d check those floats again and make sure they are operating

                    Comment


                    • #11
                      Originally posted by jimmbo View Post
                      Have you done a Cylinder Drop Test? Disconnecting a plug wire to see how much worse the engine runs. If no difference than that cylinder isn't doing its share.
                      Jimmbo: I got it idling (roughly) in a large garbage can full of water tonight and performed a drop test. Pulling the spark plug wire from either cylinder 1 or 2 has NO effect on how the motor is running. Pulling the plug wire from #3 or #4 kills the motor immediately.

                      #1 and #2 are sparking to some extent though. They'll bite you if you're not careful. (Don't ask me how I know)
                      "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
                      Koos Brandt

                      Comment


                      • #12
                        Swapped the Red and Blue pairs of wires going from the stator to the CDI switch box just now. The problem stayed with Cylinders #1 and #2. Trigger tests good with wires disconnected. Here is quote from the CDI troubleshooting manual.

                        2. If you have two cylinders not firing (either #1 and #2, or #3 and #4), switch the stator leads end to end on the switch box (swap Red with Red/White) and (swap Blue with Blue/White). If the problem moves to the other cylinders, the stator is bad. If the problem stays on the same cylinders, the switch box is likely bad.

                        At this point, I think it is evidence to support my original assessment that the switch box may be defective. Going to order one tonight and will report back.
                        "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
                        Koos Brandt

                        Comment


                        • #13
                          Originally posted by wcsd106 View Post

                          Jimmbo: I got it idling (roughly) in a large garbage can full of water tonight and performed a drop test. Pulling the spark plug wire from either cylinder 1 or 2 has NO effect on how the motor is running. Pulling the plug wire from #3 or #4 kills the motor immediately.

                          #1 and #2 are sparking to some extent though. They'll bite you if you're not careful. (Don't ask me how I know)
                          Well. from that it sounds like cylinders 1 and 2 are not firing. Since they share a carb I would be going over it very carefully. However, you say that 1 and 2 are "sparking to some extent though". Do you mean Intermittently?

                          Try spraying a bit of Fuel(50:1 mix) into the top carb while running and see what difference it makes, also redo the drop tests when adding the spray
                          Last edited by jimmbo; September 16th, 2019, 05:16 PM.

                          Comment


                          • #14
                            Sign up today
                            Will do, Jimmbo. Thanks. I'll make up some premix and spray it into the top carb. I'll be glad when I can get my buddy's boat out of my driveway, LOL.
                            "My biggest worry is that my wife (when I'm dead) will sell my fishing gear for what I said I paid for it."
                            Koos Brandt

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