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GS750 ignition timing 180 degrees out??

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    #1

    GS750 ignition timing 180 degrees out??

    Hello,

    I've got a 1978 GS750 that I bought as a non runner and have just got running for the first time. The bike starts fine (but doesn't rev). When I check the ignition timing it looks like it's 180 degrees out. The left hand set of points are opening for the second and third cylinders, but the manual says these should be for cylinders one and four. Could the timing be 180 degrees out? If so would it run at all?

    Any help or advice gratefully received.
    Lee
    Tags: None
    #2
    Just remove the rotor from the mechanical advance, turn it 180 degrees and re-install. Also check the coils, make sure they are going to the right plugs.
    1166cc 1/8 ET 6.09@111.88
    1166cc on NOS, 1/8 ET 5.70@122.85
    1395cc 1/8 ET 6.0051@114.39
    1395cc on NOS, 1/8 ET 5.71@113.98 "With a broken wrist pin too"
    01 Sporty 1/8 ET 7.70@92.28, 1/4 ET 12.03@111.82

    Comment

      #3
      Whoa, hold on a minute. Maybe I'm confused, but wouldn't 180 degrees off cause the plugs to fire at BDC? I don't see any way it could start at all being 180 off. I think what may be confusing you is that the ignition system fires the plugs on both compression and exhaust strokes, thus it could appear to you to be opening on the wrong set of cylinders.

      Comment

        #4
        If the coils leads have been swapped between 1&4 and 2&3 then it will still work with the rotor 180 degrees out. Sounds like something else is going on too. Just like a V8 if you know the firing order you can have any lead as number one, problem is when someone else works on it they are going have BPITA trying to figure it out.

        The condenser can cause all sorts of problems too. Install new points and condensers, gap then as oem, set the timing and see how she runs. Also get a wiring diagram and make sure the ignition system is correct. Also drop the bowls and clean the jets if the bike has been sitting for awhile.
        Last edited by RacingJake; 03-23-2006, 10:42 AM.
        1166cc 1/8 ET 6.09@111.88
        1166cc on NOS, 1/8 ET 5.70@122.85
        1395cc 1/8 ET 6.0051@114.39
        1395cc on NOS, 1/8 ET 5.71@113.98 "With a broken wrist pin too"
        01 Sporty 1/8 ET 7.70@92.28, 1/4 ET 12.03@111.82

        Comment

          #5
          Lee, The timing can be off 180 degrees... I am not sure if you have a points ignition or electronic but if the leads off the points or pickup coils are attached to the wrong coils, then the timing will show up 180 degrees off. On each coil, two wires are connected. One is 12VDC and the other is the timing signal from the crank. This signal is provided by the points or pickup coils. Find these wires attached to the coils and swap them. Then when you attach a timing light, your 2/3 coil will show the timing on your ignition plate correctly and the 1/4 as well. Your timing will still have to be adjusted but it won't display 180 degrees out.

          Comment

            #6
            Thanks

            Excellent, thanks for all the suggestions guys. I'll have a look at it over the next few days and see what I can find.

            Lee

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