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Suzuki gs750 1978 low compression

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    Suzuki gs750 1978 low compression

    Hello Guy's, Here is a new member Off the forum ( proud to own a Suzuki gs )

    did compression test the other day ( valves checked and all good, one was 0.09mm but guess that's no problem ).

    compression was low.( For information : did compressiontest hot, throttle full open, valve clearence good.)


    Dry. Wet
    Cilinder 1: 114 121
    Cilinder 2: 106 112
    Cilinder 3: 104 107
    Cilinder 4: 107 113

    what do you Guy's think? As I see it there is not that much difference between wet and dry.
    what can be the problem?

    Would love all information you Guy's have!

    kind regards,
    Sander

    #2
    Has it been sitting for a while? If it runs, run it a bit and recheck - valves might not be sitting properly.
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

    Comment


      #3
      Run the bike for a bit and retest. Or have you already been riding the bike for sometime? and I don't mean 100 miles.
      Rob
      1983 1100ES, 98' ST1100, 02' DR-Z400E and a few other 'bits and pieces'
      Are you on the GSR Google Earth Map yet? http://www.thegsresources.com/_forum...d.php?t=170533

      Comment


        #4
        Yup run the snot out of it and beat the engine with some speed jamming through the gears. Get those rings reseated and shaken loose again.
        MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
        1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

        NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


        I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

        Comment


          #5
          Maybe your compression gauge is faulty? There's not a huge difference between the dry and wet readings which would indicate the rings are sealing fairly well.
          Current:
          Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha )

          Past:
          VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
          And a bunch of other crap Yamahas....

          Comment


            #6
            Have not been riding it myself for alot ( 4months away from my driving licence ) , i did run it stationary for like an half an hour or so before compresson test. But i guess that's not enough? :P what do you guys mean with get them seating again? Because wet dry doesnt make a big difference as you see in the readings.

            Also the bike has 88.000km on the counter.
            So i will have to wait 4months to drive it. Suggestions to what i can do this moment?
            Thaaanks!

            Comment


              #7
              The rings seat under load as thats when the most resistance is applied to the cylinders. Ride the snot out of it and go through a lot of RPM changes and cycles. One thing that will free any Carbon sticking in the ring grooves is a 50 /50 mix of any tranny fluid and Acetone. A few ounces down each plug hole and let it set. Place a rag over the plug holes and crank it a few times to eject the fluid out when youre ready to out the plugs back in and ride it. DONT crank it with the plugs in until youve ejected the residual fluids from the cylinders first.
              MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
              1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

              NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


              I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

              Comment


                #8
                Originally posted by SanderG View Post
                Have not been riding it myself for alot ( 4months away from my driving licence ) , i did run it stationary for like an half an hour or so before compresson test. But i guess that's not enough? :P what do you guys mean with get them seating again? Because wet dry doesnt make a big difference as you see in the readings.

                Also the bike has 88.000km on the counter.
                So i will have to wait 4months to drive it. Suggestions to what i can do this moment?
                Thaaanks!
                Was it blowing a bunch of smoke, making bad noises or gutless when you rode it last? If not, then just ride it.

                I'm still thinking your compression gauge might be faulty - sometimes it doesn't take much to make them inaccurate (drop on the garage floor, etc). Maybe get another gauge to compare.
                Current:
                Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha )

                Past:
                VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
                And a bunch of other crap Yamahas....

                Comment


                  #9
                  I think he's saying that he can't ride it yet without his license. Some people frown on that, but my suggestion if that is the case, would be to have someone else run the snot out of it.
                  GSRick
                  No God, no peace. Know God, know peace.

                  Eric Bang RIP 9/5/2018
                  Have some bikes ready for us when we meet up.

                  Comment


                    #10
                    I would just ride it...they cant write a ticket until you stop !!!!
                    MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                    Comment


                      #11
                      You ran it stationary for 30 minutes? Hope you had a fan on the engine to move air through it.
                      sigpicMrBill Been a GSR member on and off since April 2002
                      1980 GS 750E Bought new in Feb of 1980
                      2015 CAN AM RTS


                      Stuff I've done to my bike 1100E front end with new Sonic springs, 1100E swing arm conversion with new Progressive shocks installed, 530 sprockets/chain conversion, new SS brake lines, new brake pads. New SS fasteners through out. Rebuilt carbs, new EBC clutch springs and horn installed. New paint. Motor runs strong.

                      Comment


                        #12
                        mrbill5491, not for 30minutes no, brother took it driving for 15min and then I kept it stationary idling for like 15 more. what Would be the concequence if you run it for long time stationary? The engine does not make lot of rpm so I would think the heat production would be minimum.
                        Or not?

                        Comment


                          #13
                          Hello Guy's,

                          I have like 400 miles on the clock since I bought the bike and did a retest of my compression. Here are the old ( 400 miles ago ) and new results in PSI ( tested it in Bar but I think you guy's don't work in that unit. )

                          Old / New

                          Cilin 1 : 115 / 116
                          Cilin 2 : 106 / 109
                          Cilin 3 : 104 / 109
                          Cilin 4 : 107 / 107

                          So as you can see, they are not much better then the old numbers. Since the bottom compression described by Suzuki is 100 PSI my question is :

                          Is this bike worth putting lot of effort and money in it?

                          Because this winter I was about to break down the carburetors and change all the rubbers/clean everything. But when I see that this all will cost me about 250 euro alone I would like to know what you guy's think of it? ( PS: not afraid to put some money in to it, but wasting money on something thats gone is a bit stupid )
                          Visually is the bike in pretty good condition. With a nice Red color.
                          Is there anything you guy's would do to it that would increase the compression and doesn't involve giving the bike a full top end rebuild?
                          Due to low compression the bike obviously is hard/not to start when it's colder, that's what bothers me the most.
                          Let me know!

                          ps: the bike has 88.000km/ +- 55000 miles.

                          Comment


                            #14

                            Comment


                              #15
                              Let me start out by saying - I don't know what the compression should read, however, if it really is low and the reading is virtually the same dry vs. wet, then it's the valves. That's engine basics 101 assuming the test was performed correctly with an accurate device.
                              Last edited by Guest; 12-29-2017, 10:47 AM.

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