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  4. CB750 scrambler project

CB750 scrambler project

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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...

    1 Reply Last reply
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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
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          • 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.

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            • 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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                • S Offline
                  S Offline
                  SpookDog
                  wrote on last edited by
                  #103

                  You mean the hole at 9 o’clock on the pic? Yeah, it could be oil bathed. Specially if the cover had a oil proof gasket. 4 strokes are ‘different’ 😜
                  I’d look into the voltage issue.

                  Louis-DT-WRL 1 Reply Last reply
                  0
                  • S SpookDog

                    You mean the hole at 9 o’clock on the pic? Yeah, it could be oil bathed. Specially if the cover had a oil proof gasket. 4 strokes are ‘different’ 😜
                    I’d look into the voltage issue.

                    Louis-DT-WRL Offline
                    Louis-DT-WRL Offline
                    Louis-DT-WR
                    wrote on last edited by
                    #104

                    @SpookDog yes I think my main concerns now is why is there so much pressure in the crankcase? Manual said 3.5L oil with a new filter..... I wonder if it's wrong and over filled

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                    • Louis-DT-WRL Offline
                      Louis-DT-WRL Offline
                      Louis-DT-WR
                      wrote on last edited by
                      #105

                      Right, I thought "oh shit the crank seal is gone"

                      Looking at all diagrams..there isn't a seal!
                      Anyone else who wants to help confirm I'm not going made... Please do 🙂

                      The oil literally returns to the sump through that window where you can see the crankshaft web.... Strange right... But makes sense why there's a "return" to the sump
                      The side cover is a sealed type so that's why oil doesn't drip out.

                      The oil is about 0.5l -.6L over filled from having the wrong information in a manual I have..

                      Manual states oil capacity (when replaced) 2.8L without filter and 3L with filter. (Dipstick still doesn't show anything... Perhaps from another bike)

                      I believe this caused there to be oil on the pulse generator = no pick up pulse.....

                      Drain the oil time tomorrow. Refill to correct level.

                      Clean up pulse generator... If still not producing 0.7v I need a new one.

                      🤞 This is the issue.

                      1 Reply Last reply
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                      • S Offline
                        S Offline
                        SpookDog
                        wrote on last edited by
                        #106

                        4 strokes always have air movement in the case/block, the pistons pumping up and down displace air. You can get over pressure from worn rings/ piston blow-by...
                        You ain’t going mad, sanity is just a learning curve 🤪

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

                          4 strokes always have air movement in the case/block, the pistons pumping up and down displace air. You can get over pressure from worn rings/ piston blow-by...
                          You ain’t going mad, sanity is just a learning curve 🤪

                          Louis-DT-WRL Offline
                          Louis-DT-WRL Offline
                          Louis-DT-WR
                          wrote on last edited by
                          #107

                          @SpookDog I think actually how this works now
                          Apparently the pulse generator is supposed to have oil in there (oil cooled)... Which is great because there is no oil seal on the crankshaft that can go wrong......

                          If you remove the cover when it's on the side stand (the only Stand I have)lots of oil will pour out...
                          Only a small amount of oil come out on the centre stand....
                          The pulse generator seems to not put out enough voltage so I've ordered a new one.

                          As I've done lots of tests it is is the pulse generator that I believe is the issue.

                          There's also supposed to be a proper gasket for the cover which I've ordered

                          The CBX 750 which is almost an identical engine have the oil filler cap on the left-hand side.

                          As the cbx750 shares a lot of parts
                          On my bike this has a cap saying "do not open"
                          On the left casing (where the oil filler is on the CBX)

                          if you open this when it's on the side stand oil will pour out as well..

                          . I'm guessing at the CBX 750 at the side stand on the right hand side.

                          1 Reply Last reply
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                          • S Offline
                            S Offline
                            SpookDog
                            wrote on last edited by
                            #108

                            I had a gsxr750 that was the same, oil cooled, 2 oil caps, total bitch to diagnose 😊

                            Louis-DT-WRL 1 Reply Last reply
                            0
                            • S SpookDog

                              I had a gsxr750 that was the same, oil cooled, 2 oil caps, total bitch to diagnose 😊

                              Louis-DT-WRL Offline
                              Louis-DT-WRL Offline
                              Louis-DT-WR
                              wrote on last edited by
                              #109

                              @SpookDog it's not even mentioned in the manual about not removing the left-hand pulse generator cover on the sidestand 🤷‍♂️

                              1 Reply Last reply
                              0
                              • Louis-DT-WRL Offline
                                Louis-DT-WRL Offline
                                Louis-DT-WR
                                wrote on last edited by
                                #110

                                I have no idea when I use the shrug emoji it changes it to a girl and the gender symbol 😂

                                After further investigation... My cdi which was sold by a bike breaker written in white paint "cb750 1997" ... I cleaned off the paint carefully and the part number just about readable is

                                MASG G
                                571U

                                Which is a cbr900!!!

                                Whether or not that's a problem, I've got another one from another spares breaker with the correct part number for the cb750 sevenfifty

                                1 Reply Last reply
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                                • CalumC Offline
                                  CalumC Offline
                                  Calum
                                  wrote on last edited by
                                  #111

                                  Keep us posted! I'm itching to hear that you've cracked this!

                                  Always Originate, Never Pirate!

                                  Louis-DT-WRL 1 Reply Last reply
                                  0
                                  • CalumC Calum

                                    Keep us posted! I'm itching to hear that you've cracked this!

                                    Louis-DT-WRL Offline
                                    Louis-DT-WRL Offline
                                    Louis-DT-WR
                                    wrote on last edited by
                                    #112

                                    Same here. Should be beasty.
                                    I knew the electrics would be the hardest part.
                                    All lights and horn was easy.
                                    Starter circuit was ok.
                                    Just the ignition circuit 😁

                                    1 Reply Last reply
                                    0
                                    • S Offline
                                      S Offline
                                      SpookDog
                                      wrote on last edited by
                                      #113

                                      It WILL fire up with a new CDI, unfortunately online buying is a fukin shark feeding frenzy of a$$hol£s all caring about one thing. The amount of times I’ve been shafted on fleabay is unreal. Brought a headlight that came without the bulb holder or rubber, the bloke had the neck to tell me that I was confusing his with another listing, conveniently after his pics were down. The only reason I nodded was cause it was complete...
                                      Another bloke changed the listing twice while I was between messaging. Once to up the price £40 then to change from 3 wire to 5wire servo! Same listing number an all...

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

                                        It WILL fire up with a new CDI, unfortunately online buying is a fukin shark feeding frenzy of a$$hol£s all caring about one thing. The amount of times I’ve been shafted on fleabay is unreal. Brought a headlight that came without the bulb holder or rubber, the bloke had the neck to tell me that I was confusing his with another listing, conveniently after his pics were down. The only reason I nodded was cause it was complete...
                                        Another bloke changed the listing twice while I was between messaging. Once to up the price £40 then to change from 3 wire to 5wire servo! Same listing number an all...

                                        Louis-DT-WRL Offline
                                        Louis-DT-WRL Offline
                                        Louis-DT-WR
                                        wrote on last edited by
                                        #114

                                        @SpookDog I know the feeling. Many sellers have lots of similar items for sale but send the wrong ones.
                                        The problem is I built this bike with parts from about 30 bikes... And no real way to test it will work together until I try

                                        1 Reply Last reply
                                        0
                                        • Louis-DT-WRL Offline
                                          Louis-DT-WRL Offline
                                          Louis-DT-WR
                                          wrote on last edited by
                                          #115

                                          I've got sparks on the plugs.... Just need 1 more part before I start up.... 💪

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