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  • Fuel sending unit adjustment

    Bought an abused Road Star. Dented fuel tank. Fuel gauge inop. Lots of issues. I noticed that a lot of guys have issues with fuel gauges and end up buying new sending units. There is very little information in the service manual so I decided to delve into this mysterious device. When the tank was full the gauge read empty and the fuel light flashed. The gauge read full at 3/4 tank and the light quit flashing. The gauge read empty with two gallons left in the tank and the fuel light came on steady. Removed the sending unit and the sending unit tested good with an ohm meter but the float went so high that the wipers came off the windings and the sending unit tested open. That explains the empty reading and flashing light when the tank is full. Flashing fuel light signals faulty sending unit. If you unplug it (green plug) you get the same indications. The sending unit has a stop that prevents the float from sweeping upwards too far with a full tank. The arm on my sending unit was bent drastically and would not contact the stop. I opened the wire end (barrel) of a crimp connector, cut off the forked end, and crimped it around the arm of the sending unit to prevent it from rising too high (see photos). A simple test with an ohm meter showed that it worked perfectly. There is no more adjustment necessary for the full reading. For the low reading I began with the premise that the light should come on and the gauge should read empty just before the main fuel supply runs out and it becomes necessary to switch to reserve. I don't need a warning light to tell me that the tank is completely empty. I want to know when I need to switch to reserve. So with tank installed, bike level, gauges plugged in (laying on a towel on the tank) and a drain hose on the petcock I drained the main fuel from the tank and watched for the low fuel warning light to illuminate. The needle will not move (more on that later) but the light will tell you when you are on empty. If it illuminates too early or doesn't illuminate unplug the gauges, drain the reserve fuel, remove the tank, remove the sending unit, and bend the float arm to suit. Reinstall, pour in some fuel, and repeat the process. It took several attempts to achieve the desired results. I took it for a test ride and the needle showed empty and the low level light came on about five miles before the engine died and I had to switch to reserve. When I filled it it read full. PERFECT!

  • #2
    The fuel sending unit (27) is a variable resistor that is wired in series with the ground wire from the fuel gauge (23). The fuel gauge is fed from a backup fuse that is not switched. As the resistance changes the needle on the fuel meter moves in proportion. I noticed that when I was trying to adjust my sending unit the needle on the fuel gauge would not change position. Even if I cycled the key switch it would not change. Then I pulled the print (see photo) and noticed a white wire from the fuel gauge to the speed sensor (18). That same white wire runs to the turn signal relay (28). Since we all know that the turn signals on the Road Stars cancel after a certain distance traveled and that distance is regulated by the speed sensor, it would stand to reason that the speed sensor can also regulate signals to the fuel gauge. An unregulated signal would allow the fuel gauge to change needle position constantly during acceleration, braking, turning, sitting on a kickstand, etc. You probably wouldn't be able to read the fuel level. So I discovered that disconnecting the negative cable from the battery and reconnecting it caused the fuel gauge to move and indicate the current level of fuel.

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    • #3
      Interesting.

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      • #4
        Damn! Don't think I've ever seen quite the dissertation on the fuel sending unit such as that. Not that I understood it, but Damn, way to go!

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        • brianmac
          brianmac commented
          Editing a comment
          Damn father PB I'm going to have to read it two or three times see if I can understand it too. So if I can see a change in EDIT OHMS in my sending unit what do I need to work on to make my gas gauge work,
          Last edited by brianmac; 3 weeks ago. Reason: homes to ohms

      • #5
        Excellent Write-up Chooch! My fuel gauge bit the dust before I owned my roadie, so this is gonna come in handy....thanks for sharing!

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        • #6
          So all this time and all the float units could of been fixed. The only fix I remember reading on the old forum was cleaning the contacts with an eraser....didnt work. Nice write up Chouch!

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          • #7
            Thanks Chooch. Was warned not to overfill her but because I know everything, last week I did. Fuel gauge went erratic for 20 kilometers and has now settled down Now I live in hope.

            Comment


            • Chooch
              Chooch commented
              Editing a comment
              I'm sure that filling your fuel tank to the top didn't ruin your sending unit. If it reads okay throughout its range and only faults when topped off then it should be easily repairable.

            • Galcanised
              Galcanised commented
              Editing a comment
              Yeah wasn't sure . Appreciate your comments

            • Galcanised
              Galcanised commented
              Editing a comment
              So is fuel gauge error a familiar concern with Roadies? Any suggestions re a blinking fuel light? Errr yes plenty of petrol in the tank.

          • #8
            Most of the problems with our float sending units are the wipers to the circuit board wear out. I believe that the alcohol in the fuel is a contributing factor for this wear.
            I have tried to locate new wipers, but haven't had any luck finding this part.
            Click image for larger version  Name:	IMG_2317.JPG Views:	0 Size:	44.5 KB ID:	114145 Click image for larger version  Name:	IMG_2316.JPG Views:	0 Size:	82.9 KB ID:	114146
            Some company makes this part and I think it would be a easy fix.

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            • #9
              My suspicion is that the owner's manual recommendation to not overfill the tank relates to the function of the rollover valves and venting. I don't see how overfilling would be strong enough to bend any of the sending unit float components. Lots of folks recommend using the techron plus concentrate fuel additive to prevent damage to the unit. It also discusses this on the side of the bottle.

              Comment


              • Chooch
                Chooch commented
                Editing a comment
                I agree. Topping off the tank shouldn't have any adverse effect on the sending unit and I don't know how the tank could be overfilled.

            • #10
              This is just my thoughts, former Yamaha electronics repair technician.
              Most of the wiper arms are good. Yes, 2 of the arms in the picture are broken off, but there are still 4 good arms, and all of the arms are in parallel for the circuit.
              Now if the broken arms rubbed the contact trace off, and the contact traces are in series, then you would have a problem, but since the arms are all in parallel, and not seeing the circuit board traces, I doubt the 2 broken arms make a difference.
              Now here is what I think. The contact traces have lost conductivity. There is a special conductive coating on those traces and yes, I think that alcohol in the fuel is the major contributing factor.to the failure of the sending unit. The traces themselves are resistive and the alcohol breaks down that the chemicals used to make the trace.

              When audio equipment volume controls got scratchy, because of dust and carbon build up, spray cleaners in and work the control that would take care of the problem.
              But they came out with a some equipment that this did not work and you had to replace the control because the conductive traces had worn off.
              All of out modern electronics have this type of circuit control. My truck and car have automatic heating and A/C control systems. The doors that control the air flow, have actuators that use this type of conductive trace material. When the doors get lost, the computer does not know what to do and it just blows the air wherever, and not in the correct vent. Could I take them apart and clean, yes, but I would be back at replacing the actuator in a couple of weeks.

              Solution? None, other than replacing the unit itself.
              2005 Silverado Midnight Star

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              • #11
                My float came completely off from the sensor and was floating around in my tank. It took about 3 hours to fish all the little pieces of metal out from the little metal clip coming apart and allowing the arm to slide out of the hole in the off white piece. I still haven't replaced the sending unit. I use the odometer and make sure I clear the trip meter every time I fill up.
                Riding Refreshes the Soul!

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                • #12
                  I read this again and again and again , so i did the layman thing and bought a new fuel tank sender unit guess what, the fuel gauge still comes up with the needle just above the empty where it was before , does mean the gauge is faulty, stuck or have i missed something?

                  Comment


                  • #13
                    Sorry you are having fuel gauge problems Moose. Let's walk through this and see if we can figure it out together. First we need to get on the same page:
                    1. When the key is off does the needle rest on the pin below the empty mark on the gauge?
                    2. When the key is first turned to the on position does the needle stroke to the full pin, back to the empty pin, and then to somewhere on the gauge between full and empty?
                    3. Is there an amber light beneath the fuel indicator either solid or flashing?
                    4. Is the sending unit installed in the tank? How full is the tank?
                    5. Is the bike operational? Have you ridden it since installing the sending unit?

                    Comment


                    • #14
                      hi there
                      1) yes below E
                      2) yes does go over then back settles on E
                      3) the amber light was flashing while fuel tank was drained when i put 2 gallons in the light went off
                      4) the sender unit is in the tank now has 2 gallons in the tank
                      5) I can start the bike and run her up but i can't ride her as I'm waiting for new brake lines

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                      • #15
                        Okay, try disconnecting the negative cable and reconnect it. Turn the key to the on position and see if the needle settles around 1/4 full.

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                        • #16
                          When the arm came off mine i drained the tank removed the sender then shook all parts out on a piece of cardboard, tweeked that spring washer that holds the arm in with two pairs of needle nose pliers and put everything back and it did work again, the wipers are forked on the ends i could see why they could wear out or break so easy, its nice to have a fuel gauge but i still fuel up by the milage out of habit , usually around 140, the light comes on right after 140 anyways

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                          • #17
                            60.00

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                            • #18
                              kind a makes me think of putting in a battery kill switch like a boat

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