79 SF ignition problem

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • BigalG
    XSive
    • Sep 2020
    • 38
    • South Portland Maine

    #1

    79 SF ignition problem

    last year i rebuilt a 79 special and one of the big mysterys was why i kept loosing spark, bike starts bucking , cuts right out, comes back backfires.... after a lot of advice i got new coils, not the issue, and i replaced the fuse box with blades. Yes that solved it and i ran the piss out of it last summer. This spring i took it out and it ran fine for a while then the old symptoms started up again. I nursed it home as if i pulled in the clutch and revved the engine it would run again for a bit. I came home and let it sit a week. Today i took it for a short ride and the symptoms are still there, runs great , then bucks, cuts out compleetly , starts back up goes a bit, syptoms starts again. I came home and tied the ignition wires blade fuse into another slot and put in a new fuse. No change. same symptoms Any thoughts are appreciated ?
  • cajun31
    Moderator
    • Oct 2003
    • 1783
    • Brandon, MS

    #2
    Originally posted by BigalG
    last year i rebuilt a 79 special and one of the big mysterys was why i kept loosing spark, bike starts bucking , cuts right out, comes back backfires.... after a lot of advice i got new coils, not the issue, and i replaced the fuse box with blades. Yes that solved it and i ran the piss out of it last summer. This spring i took it out and it ran fine for a while then the old symptoms started up again. I nursed it home as if i pulled in the clutch and revved the engine it would run again for a bit. I came home and let it sit a week. Today i took it for a short ride and the symptoms are still there, runs great , then bucks, cuts out compleetly , starts back up goes a bit, syptoms starts again. I came home and tied the ignition wires blade fuse into another slot and put in a new fuse. No change. same symptoms Any thoughts are appreciated ?
    check the wires to your timing pickup under the left crankcase cover. They are always suspect if any are broken will cause the problems you are describing. Pull on each one to see if they are broken internally.
    2 - 80 LGs bought one new
    81 LH
    02 FXSTB Nighttrain
    22 FLTRK Road Glide Limited
    Jim

    Comment

    • Radioguylogs
      XS-XJ Guru
      • Nov 2012
      • 1933
      • Presque Isle, MI

      #3
      You symptoms follow the problem Cajun described exactly.
      -Mike
      _________
      '79 XS1100SF 20k miles
      '80 XS1100SG 44k miles
      '81 XS1100H Venturer 35k miles
      '79 XS750SF 17k miles
      '85 Honda V65 Magna ~7k miles
      '84 Honda V65 Magna 48k miles (parts bike)
      '86 Yamaha VMAX 9k miles

      Previous: '68 Motoguzzi 600cc + '79 XS750SF 22k miles +'84 Honda V65

      Comment

      • Bax
        XStremely XSive
        • Jan 2016
        • 344
        • Merrimack, NH

        #4
        BigalG This is a very common issue with the XS bikes. The pickup wires copper strands break inside of the silicon rubber insulation due to the flexing imparted by the vacuum advance assembly roll.



        ---Bax
        80 SG, --- Slightly modified with EFI.....

        Comment

        • BigalG
          XSive
          • Sep 2020
          • 38
          • South Portland Maine

          #5
          ok thanks guys, i will check them out, i did repair two of them last year as well, did not think to go back there. Much appreciated

          Comment

          • BigalG
            XSive
            • Sep 2020
            • 38
            • South Portland Maine

            #6
            i checked the wires and the continuity at the cdi box of the wires.all seemed good. Does the bike need to be running in gear for the pickup wires to show symptoms? excuse my ignorance..

            Comment

            • Bax
              XStremely XSive
              • Jan 2016
              • 344
              • Merrimack, NH

              #7
              The position of the vacuum advance assembly would be the variable. Some positions there may be continuity and it open circuits in another.

              Bax
              80 SG, --- Slightly modified with EFI.....

              Comment

              • BigalG
                XSive
                • Sep 2020
                • 38
                • South Portland Maine

                #8
                so what do you recomend ?

                Comment

                • bikerphil
                  Master of XSology
                  • Jan 2008
                  • 8629
                  • South Flori-DUH

                  #9
                  The wires usually break where they are clamped to the P/U coil plate. I would undo the wires from the clamps and stretch them, if there is a break the wire insulation will stretch.
                  2H7 (79) owned since '89
                  3H3 owned since '06

                  "If it ain't broke, modify it"

                  Comment

                  • BigalG
                    XSive
                    • Sep 2020
                    • 38
                    • South Portland Maine

                    #10
                    not finding any breaks i ended up swapping my fuse box again and cleaning every wiring connection with contact cleaner that was in the area behind the fuse box. after re assembly it ran for about 10 miles flawlesly. I hope to get a longer ride to test it further this week. Thanks for the help

                    Comment

                    • jwhughes3
                      XS-XJ Guru
                      • Sep 2009
                      • 2798
                      • Home of the Alamo

                      #11
                      The breaks are inside the insulation and hard to detect. You need to move along each wire, gently pulling apart to look for “stretch” in the insulation. Once found, clip at the break, splice in a 1” flexible wire. The very flexible braided wires found in voltmeter test leads work well.
                      John is in an anonymous city with an Alamo (N29.519227,W-98.678980)

                      Go ahead, click on the bikes - you know you want to...the electrons are ready.
                      '81 XS1100H - "Enterprise"
                      Bob Jones Custom Navy bike: Tkat brace, EBC floating rotors & SS lines, ROX pivot risers, Geezer rectifier, new 3H3 engine

                      "Not all treasure is silver and gold"

                      Comment

                      • scott0757
                        Truly XSive
                        • Jun 2007
                        • 130
                        • Syracuse, NY

                        #12
                        Has anyone located a source to buy some of this type of silicone sheathed flexible wire? I would hate to cannibalize a good set of test leads for that. I just had to do another repair.
                        Past Rides:
                        1969 OSSA 250 Pioneer
                        1979 XS650 Special
                        1978 Honda CB750K
                        Current: 1980 XS1100SG

                        Comment

                        • Radioguylogs
                          XS-XJ Guru
                          • Nov 2012
                          • 1933
                          • Presque Isle, MI

                          #13




                          Click image for larger version

Name:	Wire for PIck-up Coils.JPG
Views:	70
Size:	140.0 KB
ID:	881240

                          Click image for larger version

Name:	Pickup Coil Splices.JPG
Views:	66
Size:	148.1 KB
ID:	881241

                          Click image for larger version

Name:	PIckup Wires Dressed.jpg
Views:	71
Size:	178.0 KB
ID:	881242

                          You may decide to use a smaller wire, but 20 gauge was good for me.
                          -Mike
                          _________
                          '79 XS1100SF 20k miles
                          '80 XS1100SG 44k miles
                          '81 XS1100H Venturer 35k miles
                          '79 XS750SF 17k miles
                          '85 Honda V65 Magna ~7k miles
                          '84 Honda V65 Magna 48k miles (parts bike)
                          '86 Yamaha VMAX 9k miles

                          Previous: '68 Motoguzzi 600cc + '79 XS750SF 22k miles +'84 Honda V65

                          Comment

                          • DEEBS11
                            XS-XJ Guru
                            • Feb 2023
                            • 1384
                            • Connecticut

                            #14
                            I just did this repair on my 78. Would stumble slightly just off idle when the motor was hot and the outside temp was 93°. I ran the bike at idle with the left cover off and used a small dental hook to pull on individual wires. The second I touched a wire, the bike shut off. I repaired the wire with voltmeter lead wire and small segments of shrink wrap with internal adhesive. I also modified those pinch points so the are not so rough on the wires. About 800 miles so far with no issues.

                            Comment

                            Working...