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    #1

    Misfire when hot

    Hi guys, im new here but read some useful info in the last few weeks which helped me fixed a few issues with my 81 gs 750

    But now i got a new problem. This bike is new to me so im not sure what kind of issues it had before. It starts great and runs great until it warms up...about 5 minutes into the ride it starts to misfire and lose power. At first i thought it was an ignition coil/coils but i wanted to ask for your opinions before i waste a few hundred bucks and still have the same problem.
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    #2
    Coils breaking down when hot are not unknown, so it might be. In a way, it's good that it's doing it every time, as you can quickly remove the tank and check the coil DC resistance when it starts doing it. Of course, such faults have a way of vanishing when they cool down a bit, so you'd have to be quick.
    Same applies to the pickup coils, but at least you can check the more accessible end of the harness that goes to them.
    The most obvious, and simplest things to check are the plugs, plug caps, and leads - cheaper to replace too, and should be done as a service item in any case.
    ---- Dave
    79 GS850N - Might be a trike soon.
    80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
    79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
    92 XJ900F - Fairly Stock, for now.

    Only a dog knows why a motorcyclist sticks his head out of a car window

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      #3
      I checked the resistance when cold and one coil was about 30 and the other 50-60..i dont know what that means but im guessing its not good. Also the spark plugs 1 and 4 are black and the 2 and 3 are brown

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        #4
        The spark plugs dis-coloring on both 1 and 4 indicates it's most likely spark related.
        Current:
        Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha )

        Past:
        VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
        And a bunch of other crap Yamahas....

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          #5
          Originally posted by Gru View Post
          I checked the resistance when cold and one coil was about 30 and the other 50-60..i dont know what that means but im guessing its not good. Also the spark plugs 1 and 4 are black and the 2 and 3 are brown
          You might be having meter reading problems- those are odd ohm readings.. Go here amd read step 10

          electrical_odd-n-ends
          http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17


          as mentioned, plug color says there's a problem with 1 and 4
          1981 gs650L

          "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

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            #6
            Well i got the new coils installed and still having the issue..once again it misfires only when hot...now im thinking this could be a carb problem

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