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  4. CB750 scrambler project

CB750 scrambler project

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  • S SpookDog

    If it’s connected to the ignition it could be the cause of your problem, specially if you’re neutral lights not working...

    Louis-DT-WRL Offline
    Louis-DT-WRL Offline
    Louis-DT-WR
    wrote on last edited by
    #83

    @SpookDog alt text

    Do you think that's the problem looking at this?

    To me it looks like if the neutral light is on (which it is) it should start.

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    • CalumC Offline
      CalumC Offline
      Calum
      wrote on last edited by
      #84

      So it looks like according to the diagram that the G/W wire needs to be tied to Earth if you want to bypass the side stand switch. The Y/Bl wire can just be taped up. I.E. don't complete the circuit for that.

      Always Originate, Never Pirate!

      Louis-DT-WRL 1 Reply Last reply
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      • CalumC Calum

        So it looks like according to the diagram that the G/W wire needs to be tied to Earth if you want to bypass the side stand switch. The Y/Bl wire can just be taped up. I.E. don't complete the circuit for that.

        Louis-DT-WRL Offline
        Louis-DT-WRL Offline
        Louis-DT-WR
        wrote on last edited by
        #85

        @Calum I have the sidestand switch, all plugged in. Only the indicator light isn't connected. Does that affect it? Cheers.

        Also still confused on the wires to the green or black connectors on the coils.

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        • CalumC Offline
          CalumC Offline
          Calum
          wrote on last edited by
          #86

          The light only needs to be there if the side stand is down by the looks of it.

          Always Originate, Never Pirate!

          Louis-DT-WRL 1 Reply Last reply
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          • CalumC Calum

            The light only needs to be there if the side stand is down by the looks of it.

            Louis-DT-WRL Offline
            Louis-DT-WRL Offline
            Louis-DT-WR
            wrote on last edited by
            #87

            @Calum that's what I'm thinking but if in neutral then it shouldn't Matter ,?

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            • S Offline
              S Offline
              SpookDog
              wrote on last edited by
              #88

              I can’t get my head round the diagram at the mo. There are a lot of differences from what I know. What about the diode (number 7) condition?
              I know that the live wires on the coils will only affect spark timing if wrong, they should still spark. So I’m guessing that the problem is with the side stand, neutral, cutout circuit somewhere, if there’s no spark still...
              Sorry I can’t be more help at the mo’. Too many brewskies!🤪

              Louis-DT-WRL 2 Replies Last reply
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              • S SpookDog

                I can’t get my head round the diagram at the mo. There are a lot of differences from what I know. What about the diode (number 7) condition?
                I know that the live wires on the coils will only affect spark timing if wrong, they should still spark. So I’m guessing that the problem is with the side stand, neutral, cutout circuit somewhere, if there’s no spark still...
                Sorry I can’t be more help at the mo’. Too many brewskies!🤪

                Louis-DT-WRL Offline
                Louis-DT-WRL Offline
                Louis-DT-WR
                wrote on last edited by
                #89

                @SpookDog yes it's a crappy diagram, I assume the second bulb is the neutral one.

                I've never had a diode go wrong on anything but might test it.
                I think it's the side stand ... I'll do more tests when the plug caps come.

                Thanks

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                • S SpookDog

                  I can’t get my head round the diagram at the mo. There are a lot of differences from what I know. What about the diode (number 7) condition?
                  I know that the live wires on the coils will only affect spark timing if wrong, they should still spark. So I’m guessing that the problem is with the side stand, neutral, cutout circuit somewhere, if there’s no spark still...
                  Sorry I can’t be more help at the mo’. Too many brewskies!🤪

                  Louis-DT-WRL Offline
                  Louis-DT-WRL Offline
                  Louis-DT-WR
                  wrote on last edited by
                  #90

                  @SpookDog I think if I try to crank the engine over (on the starter motor) in gear but with the clutch switch pulled in... That would also prove if the silicon diode is faulty 🤔

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                  • S Offline
                    S Offline
                    SpookDog
                    wrote on last edited by
                    #91

                    A diode only lets electric pass one way I think. I’d try a continuity/bulb test

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                    • S Offline
                      S Offline
                      SpookDog
                      wrote on last edited by
                      #92

                      Yeah, it should only show continuity one way. Do a quick google for diode testing...

                      Louis-DT-WRL 1 Reply Last reply
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                      • S SpookDog

                        Yeah, it should only show continuity one way. Do a quick google for diode testing...

                        Louis-DT-WRL Offline
                        Louis-DT-WRL Offline
                        Louis-DT-WR
                        wrote on last edited by
                        #93

                        @SpookDog thanks.. I tested the resistance and compared it to my spare one, seemed fine. I'm pretty sure it's the sidestand circuit....

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                        • S Offline
                          S Offline
                          SpookDog
                          wrote on last edited by
                          #94

                          I recon it is as well. I’d connect the side stand and clutch switch stuff all up, put it in neutral and try it with the clutch pulled in.
                          With the coil connectors, I’d try one ‘one way’ and the other the ‘other way’ if that makes sense? One of them should spark. Once they are sparking it’s easy to figure out which is the outer banks and which is inner...
                          Good luck my amigo!

                          Louis-DT-WRL 1 Reply Last reply
                          0
                          • S Offline
                            S Offline
                            SpookDog
                            wrote on last edited by
                            #95

                            a Diode is like a one way valve for electric. The live wire on the anode and earth on the cathode should have continuity (power flowing through). Reverse the wires and there should be none.

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                            • S Offline
                              S Offline
                              SpookDog
                              wrote on last edited by
                              #96

                              One other thing! Are the coils making a good earth to the frame? I don’t mean the black &white killswitch wires. I mean where the metal bolts to the frame...

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                              • S SpookDog

                                I recon it is as well. I’d connect the side stand and clutch switch stuff all up, put it in neutral and try it with the clutch pulled in.
                                With the coil connectors, I’d try one ‘one way’ and the other the ‘other way’ if that makes sense? One of them should spark. Once they are sparking it’s easy to figure out which is the outer banks and which is inner...
                                Good luck my amigo!

                                Louis-DT-WRL Offline
                                Louis-DT-WRL Offline
                                Louis-DT-WR
                                wrote on last edited by
                                #97

                                @SpookDog pulling my hair out,
                                All the diode does looking at the diagram is. When the stand is down and the bike is in gear, it won't start unless the clutch is pulled in .... But surely is shouldn't allow the starter motor to operate as that alone can knock the bike off the stand,

                                Also should the side stand light only come on when stand is down ( in gear )or all the time including neutral 🤔

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                                • S Offline
                                  S Offline
                                  SpookDog
                                  wrote on last edited by
                                  #98

                                  I don’t think it’d affect the starter. I think it’s just to stop you pulling away.
                                  I recon it should be on as long as the stand is down.
                                  How many fuses are there as well!
                                  Wish I was there to help. It’s difficult trying to diagnose hands off!...

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                                  • S Offline
                                    S Offline
                                    SpookDog
                                    wrote on last edited by
                                    #99

                                    Trouble is it could be any one of these switches:
                                    Key Ignition
                                    Handlebar kill
                                    Sidestand
                                    Clutch
                                    Neutral

                                    Or these parts:
                                    Pulse generator/pickup
                                    Fuses

                                    Or just a break in a wire.

                                    I’d start off by checking fuses, then doing continuity checks on the switches, then the wires
                                    Check for volts at the coloured coil wires, volts at pick up while cranking the starter

                                    1 Reply Last reply
                                    1
                                    • Louis-DT-WRL Offline
                                      Louis-DT-WRL Offline
                                      Louis-DT-WR
                                      wrote on last edited by
                                      #100

                                      I think I know the issue. The pulse generator had a load of oil in there. Doesn't put out 0.7v

                                      When I crank the engine I can feel pressure of air blow past the crank seal 😬 the crank seal itself might not be broken but the pressure bypasses it.
                                      I can't see this seal on fowler's diagrams

                                      All cylinders seem to have good compression so can think why the crankcase has so much pressure. Unless it's a blocked pcv.... Not sure if they have valves ....
                                      Lots of ball aches...
                                      I couldn't really test any of this before fitting the engine all together.

                                      1 Reply Last reply
                                      1
                                      • Louis-DT-WRL Offline
                                        Louis-DT-WRL Offline
                                        Louis-DT-WR
                                        wrote on last edited by
                                        #101

                                        Damn, wtf.... Surely you shouldn't have an access window to the side of the crank (bottom of engine)

                                        alt text

                                        https://i.imgur.com/7LrE6wS.gifv
                                        See the video

                                        Louis-DT-WRL 1 Reply Last reply
                                        0
                                        • Louis-DT-WRL Louis-DT-WR

                                          Damn, wtf.... Surely you shouldn't have an access window to the side of the crank (bottom of engine)

                                          alt text

                                          https://i.imgur.com/7LrE6wS.gifv
                                          See the video

                                          Louis-DT-WRL Offline
                                          Louis-DT-WRL Offline
                                          Louis-DT-WR
                                          wrote on last edited by
                                          #102

                                          @Louis-DT-WR http://imgur.com/gallery/Bf8joaa

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