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    Interesting intermittent carb over flow issue ...

    So I've been riding the 79 850G with new top end and rebuilt carbs Mikuni VM26SS and it runs great.
    I'd like some informed ideas about one issue, especially is they're different from mine!

    So carbs 3 and 4 overflow occasionally and intermittently, and rarely.

    Everything inside is either new or in excellent condition. I've checked repeatedly (and keep checking)

    After the last ride I realized it's only after the engine is very warm, after a long ride (which also means the fuel has warmed also) and after riding agressively.

    Also, after the engine cools and on the next start they don't leak... back to normal.

    It never leaks sitting, either on side stand or center stand, no matter how long it sits, even with petcock on prime. And doesn't leak when I start it and just let it run after normal warm up.

    I'm thinking it's somehow caused by warm/hot fuel? But how??

    Important fact, I don't have a secondary inline fuel filter which now I'm thinking may be a factor, even though I don't see a need for one because the in tank filter is very good. (AND there is simple so little room in there for one it's a PIA)

    Today's test will be to go for a long-ish ride at moderate pace to see if the problem recurs.

    Here's what I've got:

    1. It's somehow related to warming fuel that's causing an issue... weird right? (welcome to my world)
    2. Upon head scratching, now I think it may simply be debris getting into the carb from warming fuel and agressive riding.

    If today's test does not cause an overflow (#2) I will put an inline filter on and test that.

    Anyway that's a summary of what I've got, any ideas (especially out of the box thinking) would be helpful.
    Last edited by JoeNashville; 09-04-2021, 10:47 AM.
    1979 GS850 G
    1979 GS1000E Resto moded
    1993 Kawasaki ZR1100


    The most effective means of preventing tyranny is to illuminate, as far as practicable, the minds of the people at large, and more especially to give them knowledge of those facts. - Thomas Jefferson

    #2
    What are you riding Joe? Put your bike details in your signature line so we don't have to keep asking...

    Top right: My Profile/About Me
    -Mal

    "The only reason for time is so that everything doesn't happen at once." - B. Banzai
    ___________

    78 GS750E

    Comment


      #3
      79 850G....hmmm it could be the fuel T's between the carbs.

      V
      Gustov
      80 GS 1100 LT, 83 1100 G "Scruffy"
      81 GS 1000 G
      79 GS 850 G
      81 GS 850 L
      83 GS 550 ES, 85 GS 550 ES
      80 GS 550 L
      86 450 Rebel, 70CL 70, Yamaha TTR125
      2002 Honda 919
      2004 Ural Gear up

      Comment


        #4
        Where are they leaking from on the carbs?
        The overflow?
        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


          #5
          They leaked from the overflow. I replaced the overflow lines with new longer ones to make sure they missed the exhaust and labeled them so I could tell quickly which ones were overflowing.

          I went for a ride yesterday morning and there was no overflowing, but it was cool and I just cruised around.

          I'll probably go out Monday after work and try to duplicate the problem.
          I'd like to point my laser thermometer into the tank so I can track the temp of the fuel. I'm really curious how much the temp of the fuel varies.
          1979 GS850 G
          1979 GS1000E Resto moded
          1993 Kawasaki ZR1100


          The most effective means of preventing tyranny is to illuminate, as far as practicable, the minds of the people at large, and more especially to give them knowledge of those facts. - Thomas Jefferson

          Comment


            #6
            Sounds like the fuel level in 3 and4 are too high..Ck. fuel level and sync...Tip: clear overflow hose, turn it up next to the side of the bowl and check the actual fuel level..You can watch it in the clear tubing..Fluid seeks it's own level..Get it ?? When heated it expands and there fore overflows..Make sure they are vented to atmosphere properly..
            sigpic 82 gs1100ez 1168 Wiseco,Web .348 Cams,Falicon Sprockets,Star Racing Ported Head,1mm o/s Stainless Valves,APE Springs,Bronze Guides,etc.APE Billet Tensioner,36CV Carbs,Stage 3 Dynojet,Plenum w/K&N filter,Trued,Welded,Balanced,Crank w/Katana rods & Billet left end, FBG backcut trans, VHR HD Clutch basket,APE nut,VHR High volume oil pump gears,1150 Oil cooler,V&H Megaphone header w/Competition baffle,Dyna S,Coils,Wires,etc.Other misc.mods.

            Comment


              #7
              Originally posted by JoeNashville View Post
              They leaked from the overflow. I replaced the overflow lines with new longer ones to make sure they missed the exhaust and labeled them so I could tell quickly which ones were overflowing.

              I went for a ride yesterday morning and there was no overflowing, but it was cool and I just cruised around.

              I'll probably go out Monday after work and try to duplicate the problem.
              I'd like to point my laser thermometer into the tank so I can track the temp of the fuel. I'm really curious how much the temp of the fuel varies.
              I have had to install several heat shields on the fuel tanks and fuel lines,Crankcase vent hoses...mostly on ATVs and race bikes..
              sigpic 82 gs1100ez 1168 Wiseco,Web .348 Cams,Falicon Sprockets,Star Racing Ported Head,1mm o/s Stainless Valves,APE Springs,Bronze Guides,etc.APE Billet Tensioner,36CV Carbs,Stage 3 Dynojet,Plenum w/K&N filter,Trued,Welded,Balanced,Crank w/Katana rods & Billet left end, FBG backcut trans, VHR HD Clutch basket,APE nut,VHR High volume oil pump gears,1150 Oil cooler,V&H Megaphone header w/Competition baffle,Dyna S,Coils,Wires,etc.Other misc.mods.

              Comment


                #8
                My first GS1150's had a heat shield under the tank, not a clue if OEM or someone had added it.
                1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

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