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Suzuki Bandit 1250 Loss of Power at Low RPM

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  • Suzuki Bandit 1250 Loss of Power at Low RPM

    Hi guys,

    I have recently bought a Bandit 1250 2011 and have realised it has some issues with power deliver at low RPM. When travelling low down in the RPM range (2k - 4k) around a specific point the bike will suddenly lose all power and jerk forward slightly as the engine brakes. If I keep the throttle in the same position, the bike will jerk back and forward, quite quickly (0.5 - 2 seconds), between normal operation and engine braking. If I accelerate from this position, it will accelerate fine (without much hesitation). I think the issue lies with the fuel injectors, when keeping the throttle barely open, the fuel injectors may not be providing enough (any?) fuel, which causes sudden engine braking.

    Most notable when accelerating HARD, then rolling off the throttle until I get to the point where the throttle is barely open - less related to RPM (sometimes can be as high as 6k RPM).
    Noticeable in gears 3, 4, 5 and 6, but most notable in 4th.
    Please note the chain is within the correct slack/tension

    What I have tried so far:
    • Two doses of liqui-moly fuel system cleaner / conditioner (helped dramatically)
    • New oil and oil filter (little difference)
    • Different octane of fuel (no difference)
    • New air filter (some difference)t
    • New spark plugs (some difference)


    The problem is actually 95% fixed, just through the above servicing and riding the bike regularly to help the fuel system keep in check.

    However, if anyone knows of any other maintenance, or ways to clean the injectors please share your thoughts

    On a side note, this bike is excellent for working on, it was engineered brilliantly.

  • #2
    When was the following work last done?
    -valve clearance check
    -throttle body synchronisation
    -check + adjust throttle position sensor

    Usually part throttle problems are a mechanical imbalance in how much air is trickling into the cylinders through the idle circuits. If all the valves are in spec, and you've balanced the throttle bodies with a synchroniser, then you have ruled out obvious mechanical issues. Now you can look at the injection system. It may be getting false signals which is why it doesn't keep up at the small/precise throttle openings. The lowest hanging fruit is a maladjusted or worn TPS which will keep the ECU half a step behind what's actually happening in your engine. All the specifics of these procedures are in the suzuki service manual.

    Oh and make sure you've got no vacuum leaks anywhere. That'll make your bike run like ass regardless of how you tune it.
    Originally posted by devolved
    I just crashed into a schoolbus full of kiddies, killed them all, raped them, set them on fire and now I'm pissing on their charred remains.

    Comment


    • #3
      Fuel filter?
      Note: this may not be the universe where the above is relevant.

      Comment


      • #4
        Originally posted by wheel_of_steell View Post
        When was the following work last done?
        * valve clearance check - Probably won't do this, unlikely to be out of spec at 24k kms
        * throttle body sync - Never done, haven't done this before but I have been meaning to get the pressure check tools to do this myself
        * check + adjust throttle position sensor - Have checked and adjusted, haven't found much difference in adjustment, perhaps this is at fault here

        I've recorded a video demonstrating the symptoms


        I am going to make some adjustments to the TPS and see what kind of response I'll get. Done this before, but didn't have the right tools to check the resistance. Now I've got the tools I'll do a proper check and see how that goes.

        Comment


        • #5
          TPS is measuring:

          4.75 for Ohm1
          4.45 for Ohm2

          Measurements taken using 20k Ω setting.

          As per this guide:
          __ TPS Connector __

          `_____
          | - - - |
          --------`` <- this edge is on the outside of the bike
          1 2 3
          \.../
          Ohm1 -------------------------- 3.5K to 6.5K on bandit 1200(Measure with throttle closed)


          `_____
          | - - - |
          --------`` <- this edge is on the outside of the bike
          1 2 3
          ..|./
          Ohm2 ------------------------- %76 of R1 which is 2.66 to 4.94k(Measure with throttle open)
          The throttle position doesn't affect any of these readings. What does this mean??

          I have taken the readings while the bike is both on and off and even with the TPS unplugged the bike still behaves in the same way as demonstrated in the video.

          Comment


          • #6
            Is It........Dropping spark to one cylinder mate ?

            Edit to make some sense...or not.
            Last edited by GsxInShed; 12-05-2018, 04:49 PM.
            " Imagination is the seed of life..."

            Comment


            • #7
              Originally posted by GsxInShed View Post
              Dropping spark to one cylinder mate.
              Sorry, what do you mean?

              Comment


              • #8
                If all you have tried and tested does nothing to the symptom.

                Then it is probably not those things...

                You said that the most change was achieved with the 'fuel system cleaner'

                Is it the injector..? Or one of them..??

                The video sounds like the motor is dropping a cylinder.. IE; losing spark to one of the plugs for such a significant miss/surge.

                Do you have the old plugs? Are they in some order as to which hole they came from? What colour are they? ( I'll assume you do have them.. )

                These bikes have issues with in tank fuel pump.. ..and dirty fuel is a cause of issues in any fuel system.

                On cars I would clamp the fuel return line partially to increase fuel pressure to the injectors....where the increase will overide the blocked injector

                ( or just pull the vac line to the pressure valve..) same result ---
                " Imagination is the seed of life..."

                Comment


                • #9
                  I would suspect one or more injectors being blocked or insuficient spray at lower pressure...since the fuel system cleaner helped a lot.

                  You may also find the fuel filter in the pump.....assuming it is an electric...one is blocked. Typically Suzuki use two filters....one is an easilly replaced 't' bag low pressure side one. The other is inside the sealed pump body and Suzuki want a shit load for a new pump. You can carefully drill the old one out and install an in line one.

                  Another method is to back flush the internal filter with clean fuel...you will know this is the problem if a lot of dirty fuel comes out. Needless to say the tank will have to come off and the pump removed....one word of advice...do not re-use the rubber seal....any leaks here will be interesting to say the least...

                  Good luck
                  Smoke me a kipper...I'll be home in time for breakfast

                  Comment


                  • #10
                    If I've posted this once, I've posted it a thousand times.

                    Originally posted by Speed Dealer View Post
                    Myself and another forum member both had the fuel pumps die on our 2008 Bandits at about 50,000km. It seems to be a common thing, but today that isn't the problem.

                    Your fuel pump is STARTING to clog. It's a stupid design on the Bandits that lends itself towards blocking the moment anything foreign is in the tank.

                    Here's how to clean it. Also order a new 'teabag' filter from the dealer. You can see it in the photo below, it's black, but it should be white.

                    All the pump assembly parts below


                    This part of the assembly where i am pointing is where the pump fits into. Underneath that little hole is a mesh screen (believe me) insert a stripped end (copper) Of wire and use like a toothbrush. Insert wire from other side and repeat. You will feel the mesh screen




                    You will see gunk appearing. Wash out with boiling water. Repeat and repeat again.

                    Comment


                    • #11
                      Should mention I had this happen to me in the middle of the Nullabor so it was tank off the bike on the side of the highway.

                      Comment


                      • #12
                        Originally posted by MZ View Post
                        * valve clearance check - Probably won't do this, unlikely to be out of spec at 24k kms
                        * throttle body sync - Never done, haven't done this before but I have been meaning to get the pressure check tools to do this myself
                        * check + adjust throttle position sensor - Have checked and adjusted, haven't found much difference in adjustment, perhaps this is at fault here

                        I've recorded a video demonstrating the symptoms


                        I am going to make some adjustments to the TPS and see what kind of response I'll get. Done this before, but didn't have the right tools to check the resistance. Now I've got the tools I'll do a proper check and see how that goes.
                        Hey man. 24k is a major service interval. Should have already had that work done twice before you go chasing other wild geese. Yes, there may be other problems with the bike but most diagnostic workflows start with the assumption that all scheduled maintenance is up to date, the tank is full of fuel, you’re on a planet with oxygen etc... here’s the schedule:


                        Yes I know it’s a PITA to check the valves
                        Yes I know it’s a PITA and requires a fancy tool so sync the throttles
                        That’s why screw and locknut valves bikes are the best
                        Originally posted by devolved
                        I just crashed into a schoolbus full of kiddies, killed them all, raped them, set them on fire and now I'm pissing on their charred remains.

                        Comment


                        • #13
                          Originally posted by wheel_of_steell View Post
                          Hey man. 24k is a major service interval. Should have already had that work done twice before you go chasing other wild geese.
                          Thanks mate, well aware of the service guidelines put forth by the manufacturer. The thing is, the manufacturer tells you to inspect these things at 24k kms to cover their asses - some of the items should be taken with a grain of salt. Also it's important to note the 24k kms service guide is the last service guide in the book, so everything that has to be checked eventually will be listed here.

                          I am friends with a veteran mechanic (40+ years of mechanical repair experience) and he told me not to bother with the valves, unless something is obviously acting up. He has a CBR1000RR which has done 170k kms and still hasn't had the valve clearance checked. I am not saying that checking it is a bad thing, just it is unlikely to be out of spec at such low kms.

                          Now I don't mind doing the work, but I think it may be unnecessary for this particular problem, or at least the clearance is unlikely to blame for this problem. I will do some further research to see if this theory is correct - if I find the clearance may be to blame then I will definitely inspect it.

                          Comment


                          • #14
                            Yeh.....so don't diagnose the fault ..On Your Bike.....just rip off the tank and fuel pump....

                            if it was the valve cleances ..and it is causing a miss... the valve would be burnt already. and not fix itself when you rev/use higher RPM.. eh?

                            And you veteran mechanic mate...needs his lazy arse kicked. at least check the clearances once a year... irrespctve of k's....

                            and when you first purchase a bike second hand-- don't ever be scared to look inside a motor....could save you a fortune.

                            People only sell bikes 'cause they CBF fixin 'em...
                            " Imagination is the seed of life..."

                            Comment


                            • #15
                              Originally posted by GsxInShed View Post

                              Is it the injector..? Or one of them..??

                              The video sounds like the motor is dropping a cylinder.. IE; losing spark to one of the plugs for such a significant miss/surge.

                              Do you have the old plugs? Are they in some order as to which hole they came from? What colour are they? ( I'll assume you do have them.. )
                              Thanks mate, I appreciate the help. Unfortunately I haven't got the plugs anymore. From memory the plugs were quite clean (not overly darkened), although they may have had a yellow tinge to them. Please note the surge is only from the 2k to 3.5k rpm range while in neutral. The rest of the range is relatively smooth(ish).

                              Originally posted by GsxInShed View Post
                              These bikes have issues with in tank fuel pump.. ..and dirty fuel is a cause of issues in any fuel system.

                              On cars I would clamp the fuel return line partially to increase fuel pressure to the injectors....where the increase will overide the blocked injector

                              ( or just pull the vac line to the pressure valve..) same result ---
                              Yes my first suspicion was the injectors, but the resistance readings may suggest the TPS is also faulty - or maybe I am misinterpreting how they work. But I am starting to agree that perhaps the TPS is not the main cause of these issues. How do I pull the vac line to the pressure valve to increase pressure? Can I just pull the vacuum lines in an outward direction to increase the pressure?

                              My friend also suggests to take out and clean the fuel pump. I might give this a shot and see what results we have. Also by inspecting the pump I should have a good indicator of the contamination residue levels left behind by the fuel.
                              Last edited by MZ; 12-05-2018, 06:23 PM.

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