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flat spot at 1/4 throttle opening

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    flat spot at 1/4 throttle opening

    working on a 80 gs750e, after installing new intake boots, raising the needles 2mm's, at setting the screws at 2 full turns from seated, i have a flat spot at 1/4 throttle, it does not however, happen all the time. the plugs are a lite brown shade, and all 4 look the same color, all 4 slides seem to move freely and the slide boots do not have anyy holes in them, the problem seem to happen as i accelarate from a stop through gears, then will go away for a few miles then return,

    #2
    Sounds like the float levels are set a little too low or there is a restriction in the fuel flow. Do you have an additional fuel fliter on the bike?

    Heavy acceleration consumes the available fuel in the bowls and it takes a moment or two for that fuel to be replaced.

    Just a thought...

    Also, a plugged fuel cap vent will cause a similar condition.

    And one more thing, have you checked to see that the main fuel feed line from the petcock does not have a "high spot" in it?
    Last edited by Dave8338; 03-27-2010, 10:54 PM.

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      #3
      Is the petcock new? Fuel flow is half the battle.
      1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
      1985 GS1150ES stock with 85 Red E bodywork.

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        #4
        yes it does have a little fuel filter inline, i will remove and see what happens

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          #5
          1/4 throttle is hardly heavy acceleration. It runs fine with the throttle open farther? If so it is getting enough fuel.

          Just curious, what made you think you needed to raise the needles 2mm? How did it run before this change?
          Last edited by tkent02; 03-27-2010, 10:57 PM.


          Life is too short to ride an L.

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            #6
            petcock is disabled, meaning nothing inside and the lines have been plugged at the petcock and carb location, and trust me flow out of the tank with the line pulled off is no problem

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              #7
              Did you use washers to shim the needle? Stick another on there if you did.
              1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
              1985 GS1150ES stock with 85 Red E bodywork.

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                #8
                Originally posted by tkent02 View Post
                1/4 throttle is hardly heavy acceleration. It runs fine with the throttle open farther? If so it is getting enough fuel.

                Just curious, what made you think you needed to raise the needles 2mm?
                Now there is a good question.

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                  #9
                  one of the post i search before stated raising the needles 2mm's from stock was a cure all for old gs's so while i had the carbs off i raised them, when i bought the bike it had 4 1mm shims on each needle, the plastic shim was not there

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                    #10
                    So you just removed two of the shims?


                    Life is too short to ride an L.

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                      #11
                      when i pull away from a stop and this happens, if i open the throttle all the way it will eventually pickup and go

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                        #12
                        yes i removed 2 shims

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                          #13
                          Stock box w/filter oiled and sealed up tight?
                          Have you replaced the intake orings?
                          Carb vent tubes open and flowing freely? (I have cleaned out more than one spiders' nest in those things...

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                            #14
                            to answer the question of how it ran before was thae intakes boots were baddly worn and the airbox was not on properly so not well at all

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                              #15
                              these are cv carbs, no orings, just rubber boots with clamps

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