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V4 1987 Looper Low Compression & Backfire In One Cylinder

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  • V4 1987 Looper Low Compression & Backfire In One Cylinder

    Hi All,

    First time joining here as I have struck a bit of issue I would appreciate some advice on. I just purchased a boat from a farmer in western Qld who had it sitting in storage for a few years.

    I have a 87 V4 Looper which had cold compression of 90psi in three cylinders and 95 in the port lower (Sorry dont know the numbering.

    Overnight it sat with carby cleaner and some in the spark ports. Today I sprayed some Johnson tuner today and blasted some but not all carbon out. I believe it needs to further sit in there but would think its been exhausted out? I did a secondary comp test now it was warmed up and got 80 in most and 85 in the in the port lower again. So it dropped 10psi over the decarb or heat up.

    I looked through the spark ports and the carbon wasn't all gone, from face of piston. The plugs and leads were replaced, but after a few hours running there wasn't major build up.

    I have good running most of tme. Get to 5.5k in revs trim down with 40mph. I would think can get more?

    The fuel lines have been replaced and filter, tank has bee flushed also. Hence why I started looking into carbs and engine.

    The lower port carb with the high compression than others, spits and back fires at low idle.

    Would appreciate any advice on this as I thought the motor was in top condition. See photos attached.

    Riley
    Prop shaft Prop & Seal Carb bank showing port side

  • #2
    What hp is your motor? Get a different gauge. What boat is it on? Have you replaced tje waterpump impeller? Have you gone through the fuel system?

    Comment


    • #3
      G'day,
      your compression numbers aren't real good, sorry to say it right on xmas,
      got a mate with a different compression tester?
      yours could be dodgy,

      numbers should be well over a 100 really and be within 10-15 %

      l'd suggest a carb disassembly and cleanout, at the very least,
      there will be a buildup of old fuel inside, you will probably need to buy a carb kit and probably a fuel pump diaphragm as well...can't hurt
      RMP on ebay has a lot of different models,
      whereabouts in Qld was it

      Comment


      • #4
        Hey guys it was in Minden near Lowood. I just purchased the gauge but it was a cheapy. I wish I never bought the damn boat boat now. Thought it was in good condition.

        The motor is a 140Hp Evinrude, should be pulling bigger number than that.

        No Salt Water use.

        Ill pull the carb out one day. The amount of hours already on this has sent the wife mad.

        Comment


        • #5
          Originally posted by flyingscott View Post
          What hp is your motor? Get a different gauge. What boat is it on? Have you replaced tje waterpump impeller? Have you gone through the fuel system?
          Hi Flyingscott

          The water pump was replaced.

          Gear box oil has been done also.

          The fuel system still has the VRO pumped but bypassed.

          The fuel line have been replaced, tank flushed and new eastener fuel filter with separator.

          Comment


          • #6
            Yeh, should be higher numbers than that,
            Does it smoke a lot on start up?

            l was thinking Cunnamulla or somewhere else when you posted lol
            l'd try and find another tester,

            Comment


            • #7
              Originally posted by Tassie 1 View Post
              Yeh, should be higher numbers than that,
              Does it smoke a lot on start up?

              l was thinking Cunnamulla or somewhere else when you posted lol
              l'd try and find another tester,
              Smokes a little but thought it was just a build up, previous owner ran 40:1. Its fine once heated up.

              See photos attached guys, do you think its headed for trouble?

              Couldn't see major issues with gasket, bolts a little rusty from being in there 30years.

              Head water jacket needs a clean for sure.

              Comment


              • #8
                Originally posted by Tassie 1 View Post
                G'day,
                your compression numbers aren't real good, sorry to say it right on xmas,
                got a mate with a different compression tester?
                yours could be dodgy,

                numbers should be well over a 100 really and be within 10-15 %

                l'd suggest a carb disassembly and cleanout, at the very least,
                there will be a buildup of old fuel inside, you will probably need to buy a carb kit and probably a fuel pump diaphragm as well...can't hurt
                RMP on ebay has a lot of different models,
                whereabouts in Qld was it
                Do you think head gaskets maybe? My decarb has cleaned enough?

                Photo below shows how clean it got.

                Comment


                • #9
                  Could be just head gaskets,
                  the water jacket has a lot of corrosion and blockages for a fresh water motor,

                  looks like it's never been flushed in it's life,

                  l've got a '81 70hp block that spent most of it's life in saltwater and has nowhere near the amount of corrosion your one has...and mine wasn't flushed everytime either,

                  so, l'm guessing head gasket too

                  Comment


                  • #10
                    Originally posted by Tassie 1 View Post
                    Could be just head gaskets,
                    the water jacket has a lot of corrosion and blockages for a fresh water motor,

                    looks like it's never been flushed in it's life,

                    l've got a '81 70hp block that spent most of it's life in saltwater and has nowhere near the amount of corrosion your one has...and mine wasn't flushed everytime either,

                    so, l'm guessing head gasket too
                    Thanks Tassie,

                    See photos after I cleaned it, found the following.

                    Photo 1: Port Lower Cylinder had been replaced in 02. This is the cylindar which back fires from carby and has higher compression.
                    Port gasket in worse condition than starboard
                    There was only one bore with a slight groove and that is port upper. Photo 2
                    All the other came up pretty clean. Cant say enough also about wax and grease remover. Using it also with the OMC engine tune.
                    Photo 3 shows bubbling on port head gasket.

                    Where can I get a gasket really fast but taking into count Aussie public hols for two days?

                    How do I clean the gunk out of the water jacket? IT might explain why even with the water pump replaced, there is no real pressure during flush out of drain. Can figure it out, my other motors ran hot and alot of water pressure from the pump. In the water it seems fine though.

                    Comment


                    • #11
                      Merry Christmas by the way guys, really appreciate getting back to me.

                      Comment


                      • #12
                        Originally posted by Tassie 1 View Post
                        Could be just head gaskets,
                        the water jacket has a lot of corrosion and blockages for a fresh water motor,

                        looks like it's never been flushed in it's life,

                        l've got a '81 70hp block that spent most of it's life in saltwater and has nowhere near the amount of corrosion your one has...and mine wasn't flushed everytime either,

                        so, l'm guessing head gasket too
                        Hi Tassie,

                        Also there's not really corrosion in the water jackets it's like this gunk buildup. See clearer photo

                        Comment


                        • #13
                          No need to be paranoid about black stuff on top of the pistons.----Very normal.-----Look into cleaning that one carburetor and look for issues with crankcase compression.----Crankcase compression is different from cylinder compression.

                          Comment


                          • #14
                            Your cylinders are within 10% of each other. The fact it idles and runs to 5500 rpm does not suggest a compression issue. Get a different gauge and clean the carb as racer said.

                            Comment


                            • #15
                              Sign up today
                              Originally posted by Riley C View Post

                              Smokes a little but thought it was just a build up, previous owner ran 40:1. Its fine once heated up.

                              Clean or replace plugs (regap at .030). Run at 40:1 with good TCW-3 oil.

                              Comment

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