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  • Revs dropping under emergency braking

    I just put my bike back together today and took it for a ride and noticed the revs dropping down to about 1000-1500rpm under heavy braking, idle speed is set to 2500rpm (warm)

    I have done the following prior to putting it back together;

    - Replaced fuel tank which had heaps of rust and shit inside it
    - Replaced all fuel lines, filter and flushed the pump
    - Thoroughly cleaned the carbies with carby cleaner and inspected and adjusted float heights
    - Cleaned main jets, pilot jets and pilot jet mixture screws
    - Oil and Oil filter change
    - New spark plugs

    Never done this before and I've heard its something to do with the floats in the carbies, and my carbies aren't in the best nic either, needs a rebuild.

    PS, anyone know where I can buy a rebuild kit for a Mikuni BSW27 carby?

    Cheers,
    Martin

  • #2
    Idle speed is WAY too high... unless im wrong it should be round 1400 or so.

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    • #3
      Its set to about 1800rpm cold, but when it warms up, it runs at about 2500.

      the manual recommends between 1500 - 1800rpm.

      Comment


      • #4
        i agree. that idle speed is ridiculous
        Morley Tyrepower

        (08) 9275 3394

        [email protected]

        For all your car needs

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        • #5
          Idle mixture screws too rich. Try putting them in half a turn (you can always move them back)
          Adjust idle speed when warm only.
          Being an Australian is not an excuse for being dumb and racist.

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          • #6
            It should be 1500-1800 when warm, and use the choke to raise it when cold.
            For LAMS information and resources - http://www.perthstreetbikes.com/foru...thread-156358/
            For LAMS discussion and to ask questions - http://www.perthstreetbikes.com/foru...thread-143289/

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            • #7
              The choke doesn't work on my Across, it will rev out only when the choke is on full and will quickly die after about 3 seconds.

              I don't even bother with it, and my bike has had starting difficulties so that is why my idle speed is set that high

              But apart from the high idle speed, do you guys have any other idea of what can be causing the revs to drop.

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              • #8
                ^^ could be running excessively rich (maybe to do with the apparently busted choke), and suddenly snapping the throttle off causes it to have a large excess of fuel in there (and no air to burn it) that strangles it

                had similar problems when i had an atmo bov on my car and an AFM (rather than map sensor). the bov would bleed air that had already been measured by the AFM, excess fuel would be fed to the motor, and it would want to stall.


                It doesn't happen to chew through a heap of fuel by any chance? I'm guessing perhaps the idle speed was set high to try and get around the problem and that the high idle is not in itself the root cause.

                My money is on the bike running way rich due to busted choke... or as mentioned, simply way too rich on the mixture screw... Could also be float level too high(? not a carby expert).

                Either way, i'd put money on it running too rich, one way or another.
                “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

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                • #9
                  maybe a fuel tap issue as well?
                  Morley Tyrepower

                  (08) 9275 3394

                  [email protected]

                  For all your car needs

                  Comment


                  • #10
                    ^^ if it starts running leaner the revs will actually climb before it stalls, rather than choking to death
                    “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

                    Comment


                    • #11
                      Well I set the pilot mixture screws to run a little rich for easier startings, and I'd assume that would be the main culprit there.

                      I haven't tested fuel consumptions after the carrying out the repairs/service but beforehand, I was getting about 130km to the tank which isn't good at all.

                      The spark plugs were a just a tad carbon fouled so I decided to replace all the plugs and will pull them out in the next week or so to see what they are like.

                      How would I go with fixing the choke? The Across has a fuel enricher which adds more fuel instead of restricting the airflow.

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                      • #12
                        Just readjusted the idle pilot mixture screws, will go for a ride tomorrow and see if it still drops.

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                        • #13
                          Very handy rule of thumb works for cars bikes chainsaws and whipper snippers*
                          give a quick snap of the throttle - on - off
                          Goes back to idle - perfect
                          Hangs high for a second or two - lean
                          Goes back to idle and dies off/stumbles - rich

                          Try it.... it works
                          *If symptoms persist contact your motorcycle health care professional
                          Being an Australian is not an excuse for being dumb and racist.

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                          • #14
                            The pilot mixture screws was what I was adjusting and I was adjusting them to this:

                            1.5 turns = default setting
                            2.0 turns = rich

                            When I went to readjust it to the default setting the night before, It started okay and everything throughout the night but the morning following, it would not start at all.

                            The starter motor just kept cranking and cranking with no evidence of the engine kicking over.

                            So I set it to 3.5 turns which is extremely rich and it started perfectly fine that afternoon but was running really rough so I reset it back to 2.0 turns which was what I had before and is what we think is causing the revs dropping problem.

                            So yeah, 2.0 turns leaves me with my bike running rich and when I went for a ride yesterday, my mate behind me said it my bike was putting off alot of fumes which he could smell.

                            Any ideas of why 1.5 turns won't let my engine kick over?

                            Comment


                            • #15
                              Different jets do provide fuel at certain rev ranges.
                              Pilot jet is for very low revs all the way up to WOT.
                              they "interrelate" and play their part in the overall fuel delivery
                              If it will not iddle without choke then pilot jets do not function (Blocked pilot and or airbleed)
                              Carburators are a precision instrument.
                              that it does run on choke and your plugs are black seems to bear it out.
                              carbie "rebuild" is more than spraying carbie cleaner around and having a wee look at it sadly.
                              Depending on how far you took the carbies apart and maybe by holding them with the float bowl off ,altering the set fuel levels or reinstalled something in the wrong way.
                              A start from scratch excercise might need to be performed.
                              Also make the choke function again it is an intergral part of running your bike.

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