cagimaha Posted June 8, 2012 Report Share Posted June 8, 2012 Hi All, Seeking some forum wisdom in diagnosing the cause of a problem I'm having. The bike is a 1990 Suzuki GSXR750L and I came to start it on Wednesday morning to go to work to find it would turn over fine but not start. A quick check revealed that there was no spark. I've checked the fuses and all of the other connectors,relays, diodes etc. under the seat, none of them made a difference. Whilst poking around I noticed that wiggling the wiring loom with the ignition on made the tach needle intermittently jump and sometimes hang at around 1,000 RPM. The bike will sometimes fire once or twice, maybe even run for a short time but it then drops dead, there's no hesitation. Assuming I had a short in some of the wiring relating to the CDI or coils I opened up the loom to check the splice/junction connections in there and used the multimeter to check I had a decent +ve feed and earth for the CDI and that the coils had a +ve feed. Am I correct in assuming that the signal feed to the coils should be a +ve 12V then to trigger the spark the CDI drops the feed to earth? As I couldn't find anything wrong with the multimeter I tried "jumping" the wires to the CDI by powering it straight from the fusebox and use seperate wires to send the signal to the coils. This still made no difference. The thought then occurred to me that my CDI may have expired, I tried a CDI from a GSXR1100K on it and it was exactly the same. In my albeit limited experience, a CDI failure is total rather than intermittent however I guess it is possible I've got two duff CDI's. I've never used the 1100 CDI before and it's also possible that the root cause of the problem has fried my original CDI and now the 1100 one as well... Anyone got any ideas as to what is causing this? Any help/derision much appreciated, Ben Link to comment Share on other sites More sharing options...
lorenzo Posted June 9, 2012 Report Share Posted June 9, 2012 Complete guess, but if you've ruled out the getting the signal from the ecu to the coils part, then try the signal into the ecu part: have a look at the timing rotor and associated wiring? Link to comment Share on other sites More sharing options...
cagimaha Posted June 9, 2012 Author Report Share Posted June 9, 2012 Forgot to mention I've had a look at that, the manual lists a resistance test between the two wires from the signal generator, this was within spec. Also if you spin the motor over on the starter with the wires disconnected the multimeter detects an AC current. I spent all day yesterday looking at it. gonna have a look again in a minute. Gonna try bypassing all the sidestand shit just to make sure it's not that... Link to comment Share on other sites More sharing options...
BudgetBoy Posted June 9, 2012 Report Share Posted June 9, 2012 probably silly but have you tested the kill switch? Link to comment Share on other sites More sharing options...
cagimaha Posted June 9, 2012 Author Report Share Posted June 9, 2012 The kill switch itself is fine however I think that the problem may be in the wiring associated with the kill switch/sidestand switch setup. Because it's so intermittent it's hard to catch the fault with the multimeter if you know what I mean. The investigation continues... Link to comment Share on other sites More sharing options...
Andy J Posted June 10, 2012 Report Share Posted June 10, 2012 I had a similar problem on my 750M. It would run fine but the tacho had a mind of its own. I finally found that the loom had worn through and was earthing on the frame by the headstock when i turned the bars. It seems its a common problem on slingys. Link to comment Share on other sites More sharing options...
gurninman Posted June 10, 2012 Report Share Posted June 10, 2012 I had a similar problem on my 750M. It would run fine but the tacho had a mind of its own. I finally found that the loom had worn through and was earthing on the frame by the headstock when i turned the bars. It seems its a common problem on slingys. +1 - I had the very same thing on a 750K - the initial problem was a bad on the starter motor . Once that was sorted, I had the problems mentioned above and found it to be the loom worn through near the headstock Link to comment Share on other sites More sharing options...
cagimaha Posted June 10, 2012 Author Report Share Posted June 10, 2012 I'll go check that out now, I have actually replaced the loom on this bike last year because it had done exactly that. Obviously I replaced it with another second hand loom though... Link to comment Share on other sites More sharing options...
Andy J Posted June 10, 2012 Report Share Posted June 10, 2012 On the plus side, if it is that then that part of the loom is available seperately. I got Avionics at work to fix mine! Link to comment Share on other sites More sharing options...
cagimaha Posted June 10, 2012 Author Report Share Posted June 10, 2012 Crisis now averted, just in case anyone wants to know. If the tach feed wire is earthing itself on the headlight bracket then the CDI won't send a signal to the coils. Job jobbed! Link to comment Share on other sites More sharing options...
Smiled Posted June 16, 2012 Report Share Posted June 16, 2012 I shall bare this all in mind...... Link to comment Share on other sites More sharing options...
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