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Force 125, thought I had a bad reed valve

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  • Force 125, thought I had a bad reed valve

    So, end of the season, brought the family on the boat, had a gunshot like backfire that destroyed the rubber exhaust boot. Couldn't get the engine to run without the hood off, and it didn't run that great. Used the trolling motor. Brought it back out and it ran, but a bit rough, I could hit 38 mph with it, which is pretty normal, but the engine would run up the rpms and then drop them and surge. Actually had the engine quit for a moment like I had forgotten to open the vent on the fuel tank...started right up and kept running. Last time out, had a terrible time keeping it idling, would die when put into gear. Midrange cruising seemed pretty smooth, but it would still surge, just not as much during WOT.

    So, I put it in my tank of water, with muffs and water from the hose ( seems to be the closest I can get to lake pressure ) and checked spark. I was getting spark on all cylinders, very strong snapping arc. However, I did a cylinder balance test and found the 3rd cylinder down from the top didn't change the operation, so I am running on 3 cylinders. A compression test showed pretty equal pressure in each cylinder ( my starter is needing replacement, so I couldn't get really good cranking readings. So, I figured that I might have a reed problem, since the lower carb was dirty with fuel/oil residue. Well, I pulled the carbs and reed valves out and they all physically appear perfect. I didn't see any distortion, any cracks. I did see milky oil in the passage just inside the block, but I can't be 100% certain of a bad head gasket as I had the cover off the engine and it had rained 2 nights before. I had the covers off the front of the carbs, though I suspect not much moisture would get in that way, particularly since the motor was trimmed up for trailering.

    It had been running great prior to the backfire ( literally like a gun...scared everyone half to death ). I was able to troll for quite some time without any hesitation or loading, changing gears was smooth and never had an issue with the engine quitting. Something happened during that backfire and I can only suspect the head gasket at this point, but before I drop $40 on the gasket, I hoped to gleam some insight here first...perhaps a few nods in that direction , or something else I can check before I commit to replacing that gasket. I have photos on my phone that I can upload if there is anything you want to see.
    my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
    Official Tri Hull Club thread

  • #2
    #3 operates the fuel pump.
    ​The backfire could be the diaphragm in the pump is damaged?
    ANY drops of water on the plugs? NO then the head gasket might be ok.
    ​ONE drop and it shows you have a problem with the gasket.
    I had a small miss and the compression was 145 on all cyl.
    ​Saw a tiny spot of water on 1 plug.
    ​Removed the head and found a bad spot about 1/16" on the gasket.
    Replaced and it ran great.

    ​Each cyl has a intake port cover, the boom could have blown the gasket out.
    ​Not sealing the port(sucking air) causes poor idle, backfiring, poor performance.
    The pump is mounted to the #3 port cover.

    ​Start the motor, on muffs or in the water.
    ​Spray starting fluid around the intake ports and the carb base.
    ​If spraying makes a change in the way it runs? then the gasket is probably bad??
    ​Resealing can be tricky once they've been blown.
    ​You might need silicone on the gasket to make it seal.



    Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
    ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

    In Scenic , Beautiful San Sebastian by the sea Florida

    88 Bayliner 21CC 2001 Mercury 225 HP EFI

    Comment


    • #3
      I have new gaskets coming, the reeds are out currently and it dawned on me this morning that I may not have released pressure on the tester when I checked the cylinder. Can I do a compression test without the Reed assembly on?
      my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
      Official Tri Hull Club thread

      Comment


      • #4
        I wouldn't recommend it although it can be done as long as you spray fuel oil mix in each cylinders for each cranking. As Jerry said, check on the fuel pump diaphragm before going any further. And the other issue is the milky fluid in the crankcase cavity. This cannot be from the rain especially if the engine was tilted for trailering and the reeds fully intact.

        That said, there's a good chance the exhaust gasket is damaged leaking water into the cylinder. Personally, this will be the last item I will check as it's really a pain to work on.

        Comment


        • #5
          Looking at the exploded parts diagram, it appears that the exhaust gasket you are talking about should affect all cylinders equally, so I'm going to suspect that last, and it does look like a real PITA. What I'm not understanding is why there is focus on the fuel pump, considering that I have no power only in one cylinder. I'm not sure I understand its relevance to the dead cylinder. My reed and carb gaskets should be here next week, ( as well as the new starter ) so I think I will hold off until I can reinstall the reeds and carbs to seal up the block properly. My lack of fully understanding the working relationships of 2 cycles is hindering my personal diagnostics in regards to figuring out how each component plays a part/affects the engine as whole.

          I'm open to suggestions though, I may question motives based on my wanting to understand WHY that direction is pointed to, not that I am whole sale discounting it as an avenue of diagnostics. My access to gaskets is about a week away, so I'd prefer to not disturb anything unnecessarily. If I could have gotten my stupid USB endoscope to work well enough, I would have just probed the reeds through the carbs and probably had not even pulled them out for inspection. However, that being said, at least I can rule that out, and I have the opportunity to look deeper into the crankcase via the reed openings.
          my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
          Official Tri Hull Club thread

          Comment


          • #6
            The fuel pump is operated by #3 cyl. That' seems to be the problem area????
            IF??? the pumps diaphragm is bad, it dumps fuel into the cyl.
            That overloads/floods that cyl. and kills it.
            From my previous post:
            "Spray starting fluid around the intake ports and the carb base.
            ​If spraying makes a change in the way it runs? then the gasket is probably bad??
            ​Resealing can be tricky once they've been blown.
            ​You might need silicone on the gasket to make it seal."
            ​You can over tighten the screws holding the port covers.

            ​One backfire, cough or stutter can blow the port cover gaskets.
            ​#3 if the diaphragm is bad that can make the gasket go bad when it coughs stutters or backfires.

            The exhaust chest gasket can affect just 1 cyl.


            Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
            ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

            In Scenic , Beautiful San Sebastian by the sea Florida

            88 Bayliner 21CC 2001 Mercury 225 HP EFI

            Comment


            • #7
              Okay, I think I get a clearer picture of what you are talking about. I just did a quicky compression test without the reed valves and I was seeing 75psi on every cylinder, which I am going to assume is going to give me a clean bill of health in regards to cylinder #3 I think I will just order new fuel pump parts, for as much as I try, I haven't been able to fill up every time with Non OXY fuel. The fuel pump doesn't look like it's been serviced recently, so it's probably not a bad idea to give it a little love anyway...not to mention if it is bad, it's a cheap fix. I may still order the head gasket as well, since the boat is going to be down anyway...Not sure yet though....

              Now, when you say the exhaust chest gasket, are you talking about the side cover, or the one on the bottom of the motor that requires removing the power head?
              my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
              Official Tri Hull Club thread

              Comment


              • #8
                So, I pulled the pump off and apart, there's a tear on the larger part of the diaphram....glad to find it too. The whole picture becomes much clearer when I think about how the backfire happened, how the cylinder has compression and spark but no power. I am ordering parts as soon as I am done writing this and once I have the boat back together completely, I will report back the results.
                my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
                Official Tri Hull Club thread

                Comment


                • #9
                  Side cover.
                  The head gasket can be a BIG job??
                  The screws get seized and twist off. If you don't need to fix it?? don't.
                  ​So it was the diaphragm like I said.
                  ​If it's a fresh water motor? then the job should be a bit easier but can still be a nightmare.


                  Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                  ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                  In Scenic , Beautiful San Sebastian by the sea Florida

                  88 Bayliner 21CC 2001 Mercury 225 HP EFI

                  Comment


                  • #10
                    Yes, freshwater motor. At this point, since the problems I had had and was having all directly relate to the fuel pump problem with the cylinder, I am proceeding with replacing the fuel pump diaphram/related parts and reinstalling the reeds/carbs with new gaskets.

                    On that note, is there a trick to getting the reed valve intermediary plate loose from the gasket without damaging/cracking the thing. It's pretty tight, and I don't want to ruin a part that I cannot replace without a lot of trouble.

                    Wish I had just come here first and posted before I started tearing into this thing, but sometimes that's how you have to learn...the hard lessons stick a little better than the easy ones.
                    my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
                    Official Tri Hull Club thread

                    Comment


                    • #11
                      Not sure what your talking about?

                      The reed block is held on with 2 screws. The gasket might be covering them.
                      When you reassemble there is a tiny hole in the plate.
                      Make sure it's pointing down.


                      Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                      ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                      In Scenic , Beautiful San Sebastian by the sea Florida

                      88 Bayliner 21CC 2001 Mercury 225 HP EFI

                      Comment


                      • #12
                        Separating the plate between the carb adapter and the reed plate. I managed to get them off with a little patience and a wood chisel and a small hammer in the old gasket. I will look at the assembly again, I wasn't aware of the hole, thanks for that. What is it's purpose? Just an indexing mark?
                        my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
                        Official Tri Hull Club thread

                        Comment


                        • #13
                          Ah, I found it. Looks like it would be really hard to install it the wrong way, but it's good to know what to look for.
                          my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
                          Official Tri Hull Club thread

                          Comment


                          • #14
                            I think it can be installed as a unit upside down????(maybe???)
                            The hole is a drain for fuel that might get accumulated, it will drain down and not build up.


                            Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                            ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                            In Scenic , Beautiful San Sebastian by the sea Florida

                            88 Bayliner 21CC 2001 Mercury 225 HP EFI

                            Comment


                            • #15
                              Sign up today
                              Yeah, it is only able to be installed one way, the bolt holes index it so you can't screw it up. I'm probably going to have to rebuild/clean the carbs now. I got it together, put it on muffs, got it to start, it ran pretty good...I could tell all 4 cylinders were banging again. Took it to the lake and I lost power and had to paddle the boat to the dock the last 10 ft. Since I didn't have an inline filter between the pump and the carbs ( I will now ) I can't guarantee that nothing got into them and screwed them up. It was running like it was misfiring though. I am going to check the basics again, but I'm not really sure where I need to look other than the carbs. When I was on the lake I realized that I had shifted the carb synch linkage and it was keeping the throttle open so the idle was way high. I adjusted that and started having some stalling issues. It would sound rough through the lower range of RPM and then once got out of the idle circuit, it would clean up and run better. Near the end of my fiddling however, WOT wouldn't give me anything, felt like I was dragging an anchor on the bottom. Seems to me that since I messed with the fuel system, that I may have to clean out the carbs. I can't imagine that I did anything wrong installing the reed valves....that went smoothly, unless I missed a detail that wasn't covered in the book.

                              I'm kind of at a loss at the moment. Frustrated too, especially since it was running nicely at home, I let it cool down and got my permanent fuel tank installed and the restart was good, other than that I did have a pop through the exhaust. I dunno, maybe I've got a timing problem? I need to focus and diagnose this properly, but I'm at a bit of a loss. I am going to start at the basics and work my way through it.
                              my thread here,My Shareproject page,Part 1,Part 2,Part 3,Part 4
                              Official Tri Hull Club thread

                              Comment

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