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    GS850 #4 cylinder not firing

    So my bike restore is not going according to plan right now. It is a 1979 GS850 which was a "barnfind" and hadn't been run for 20 years. I have had the carbs off a couple of times and they have been cleaned using an ultrasonic machine plus some elbow grease and fine wire. The carbs were not "terribly" grungy but had a fair bit of dried fuel residue etc. Long story short is that the #4 cylinder refuses to light. Symptoms are:
    -cool exhaust header and popping/backfire which seems to be due to fuel starvation however I have checked these things.
    -compression is very close to the same on all 4 cylinders, 105lbs with a push in tester
    -switched the spark plugs with one from a working cylinder (no change)
    -switched plug wire caps (no change)
    -tried spraying flammable spray around the carb mounts (no change)
    - flammable spray directly into the carb throat (no change)
    -spark seems to be present and visible with the plug pulled
    -#4header much cooler than the other 3.
    -mixture screw set at 1 & 3/4 turn out-no difference in response if it is adjusted in or out unless it is closed entirely
    I will be taking the carbs off tomorrow for the third time and wondering if anyone has any suggestions. This is driving me crazy. Going to clean the #4 carb one more time but this has me and my mechanic buddy baffled.
    Any advice?
    Jonesz

    1979 GS850 current project
    1978 GL1000-naked
    1983 GL1100-Aspencade stripped
    1999 Valkyrie Tourer-long ride bike

    #2
    My suggestion is to clean the carbs properly per the VM rebuild guide on Basscliff's website. Shortcuts are long cuts so just get on with it and ungang, soak in carb dip, replace all the O-rings, etc.
    Ed

    To measure is to know.

    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

    Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

    KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

    Comment


      #3
      What Ed said, plus the fact that you don't realize you have two idle mixture screws points to the carbs not being clean
      1978 GS 1000 (since new)
      1979 GS 1000 (The Fridge, superbike replica project)
      1978 GS 1000 (parts)
      1981 GS 850 (anyone want a project?)
      1981 GPZ 550 (backroad screamer)
      1970 450 Mk IIID (THUMP!)
      2007 DRz 400S
      1999 ATK 490ES
      1994 DR 350SES

      Comment


        #4
        Thanks guys. Found the excellent article on Rebuilding VM Carbs by Paul Musser on the BikeCliff website.That will be a huge help. Will get back to you after doing another thorough cleaning.
        Jonesz

        1979 GS850 current project
        1978 GL1000-naked
        1983 GL1100-Aspencade stripped
        1999 Valkyrie Tourer-long ride bike

        Comment


          #5
          Originally posted by Big T View Post
          What Ed said, plus the fact that you don't realize you have two idle mixture screws points to the carbs not being clean
          Agree. And make sure the pilot fuel screw tips are not broken off in the carb body.
          Ed

          To measure is to know.

          Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

          Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

          Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

          KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

          Comment


            #6
            Originally posted by Nessism View Post
            Agree. And make sure the pilot fuel screw tips are not broken off in the carb body.
            Well you are a Suzuki whisperer!! Took the carbs out and started with # 4 which was the problem carb and going by the DIY article on Bikecliff & your heads up found that the pilot fuel tip was indeed broken off and lodged in the carb body. Does anyone have a clue or tip to get that broken piece of the pilot fuel screw out of the carb body without destroying it size/shape wise? Or am I now looking for a new carb body? Tried a lot of things to dislodge it but no joy so far and like I say can't be too aggressive.
            Jonesz

            1979 GS850 current project
            1978 GL1000-naked
            1983 GL1100-Aspencade stripped
            1999 Valkyrie Tourer-long ride bike

            Comment


              #7
              Go back to Basscliff's website and look for the tutorial on how to remove the tips. It's a very common problem.
              Ed

              To measure is to know.

              Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

              Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

              Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

              KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

              Comment


                #8
                Thanks Ed you may have saved my sanity today. Will let you know how it goes tomorrow. We had tried all kinds of shorter thin/sharp objects but they all bent rather than punch the tip out.
                Jonesz

                1979 GS850 current project
                1978 GL1000-naked
                1983 GL1100-Aspencade stripped
                1999 Valkyrie Tourer-long ride bike

                Comment


                  #9
                  Well the tip of the pilot screw is now out. Didn't use exactly the method on bikecliff but used a piece of sewing needle cut off, held in a pair of needle nose vise grip pliers, inserted in the shallow depression/hole in the carb throat and with a flat blde screwdriver pushed on the backend of the needle and out came that tiny bit of brass pilot screw.
                  Now it appears I am looking for a pilot fuel screw. Anyone have any good results with an aftermarket screw. Seems they are no longer available OEM. or maybe I can't find a part #. On amazon there is this one but I am kind of leery about aftermarket parts after reading about rebuild kits:
                  Find many great new & used options and get the best deals for KAWASAKI 16014-018 SCREW,PILOT ADJ. KZ650/900/1000 SUZUKI GS550/750/850/1000 at the best online prices at eBay! Free shipping for many products!

                  Thanks for the help so far.
                  Jonesz

                  1979 GS850 current project
                  1978 GL1000-naked
                  1983 GL1100-Aspencade stripped
                  1999 Valkyrie Tourer-long ride bike

                  Comment


                    #10
                    Pattern screws will do the job as long as the taper is machined on centre.
                    Here's a full set that i know are good and come with new springs and 'O' rings.
                    SUZUKI GS750 GS850 GS1000 MIKUNI FUEL MIXTURE SCREW KAWASAKI PILOT MIXTURE SCREW | eBay
                    Mikuni Viton Choke Plunger Seat Renewal.
                    VITON Choke plunger seals .KAWASAKI Z1,Z900,Z650,Z1000,Z1R,SUZUKI GS1000,GSXR,RF | eBay

                    Air Corrector Jets for Mikuni VM 24, 26 and 28mm carbs .
                    https://www.ebay.co.uk/itm/254380193...84.m1555.l2649



                    sigpic

                    Comment


                      #11
                      This should work...https://www.siriusconinc.com/pro-det...roduct_id=4245
                      Ed

                      To measure is to know.

                      Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

                      Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

                      Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

                      KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

                      Comment


                        #12
                        Originally posted by Nessism View Post
                        Not a great description that they give - "Pointy type air screw" - when it's actually a fuel screw.
                        Mikuni Viton Choke Plunger Seat Renewal.
                        VITON Choke plunger seals .KAWASAKI Z1,Z900,Z650,Z1000,Z1R,SUZUKI GS1000,GSXR,RF | eBay

                        Air Corrector Jets for Mikuni VM 24, 26 and 28mm carbs .
                        https://www.ebay.co.uk/itm/254380193...84.m1555.l2649



                        sigpic

                        Comment


                          #13
                          Thanks Ed and Zed. Really appreciate the help.Went with the one from Siriusconinc.Hopefully the shipping via Fedex will be the fastest. Will let you know how things work out. Can always go with the other ones if this doesn't go according to hoyle!
                          Jonesz

                          1979 GS850 current project
                          1978 GL1000-naked
                          1983 GL1100-Aspencade stripped
                          1999 Valkyrie Tourer-long ride bike

                          Comment

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