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Can the main jet wear?

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    Can the main jet wear?

    I have got a GS400 which has run about 65.000 miles
    I have problems getting de idle speed correct. I have checked and ajusted alle carb parts and all is according the manual. Is it possible that the main jet is worn and needs to be replaced by a new one or any other part of the carb (needle etc).

    #2
    did you adjust the air screws? how are the pilot jets?

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      #3
      Yes I checked the pilot jets but could not get it idling on a constand low speed

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        #4
        In theory it is possible that they could wear. In reality, it is highly unlikely. More likely scenarios include dirty/blocked passages, adjustments (which you have been working on) and synching the carbs.

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          #5
          Yep

          I totally agree with "The Kid". Replacing properly sized jets is usually a waste of time and money..but getting the carbs cleaned and synched is a 'sure fix' for so many problems.:-|
          1980 GS1100E....Number 15!

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            #6
            The main jets aren't going to wear from fuel flow. They can get plugged/varnished up from old fuel and dirt/rust though.
            If your carbs have the pilot circuit feeding through the main jet, then the poor idling may be from partially dirty mains. It could also be several other things.
            Dirty pilot circuit could do the same thing. Dirty carbs in general.
            Mixture screws adjusted wrong.
            Dirty air filter.
            Poor spark.
            Poor compression/burning oil.
            You could be describing an intake leak too. Does the bike idle significantly higher from cold to hot?
            And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
            Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

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              #7
              my vote is intake leak.
              Yamaha fz1 2007

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                #8
                when was the last valve adjustment???

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                  #9
                  I also vote for intake leak.

                  How're the o-rings?



                  Also check the airbox and the airbox/carb boots.

                  And kudos to whoever put 65,000 miles on a GS400 and to you for keeping it going! You gotta ride 'em to keep 'em alive.
                  1983 GS850G, Cosmos Blue.
                  2005 KLR685, Aztec Pink - Turd II.3, the ReReReTurdening
                  2015 Yamaha FJ-09, Magma Red Power Corrupts...
                  Eat more venison.

                  Please provide details. The GSR Hive Mind is nearly omniscient, but not yet clairvoyant.

                  Celeriter equita, converteque saepe.

                  SUPPORT THIS SITE! DONATE TODAY!

                  Co-host of "The Riding Obsession" sport-touring motorcycling podcast at tro.bike!

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                    #10
                    Sounds like intake orings to me too.... One of the easiest fix's, but for some reason always neglected.
                    1980 Gs550e....Not stock... :)

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                      #11
                      Originally posted by Guus de Jong View Post
                      I have got a GS400 which has run about 65.000 miles
                      I have problems getting de idle speed correct. I have checked and ajusted alle carb parts and all is according the manual. Is it possible that the main jet is worn and needs to be replaced by a new one or any other part of the carb (needle etc).
                      The main jets have nothing to do with your engines idle (or lack of). The pilot jets, and the air mixture screws dictate your engines idle.
                      You could also have a bad inlet needle and seat.

                      Comment


                        #12
                        thanks

                        Thank you all for the suggestions
                        Conclusion for me is not to replace the jet. I have replaced the O rings a few months ago so no false air. I cleaned the carb too.

                        What I have not done yet is getting them synched. I will try that first.

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