1990 intermittently running very rough

Discussion in '3rd & 4th Generation 1990-1997' started by R89B, Jun 1, 2021.

  1. R89B

    R89B New Member

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    Hi all, I've been a long time lurker on the forum but this is my first post.



    I've got a 1990 model VFR750 that has a bit of an odd issue.



    Back last year I was out for a ride and about an hour in it started running really rough, almost like a misfire. A few weeks later I gave it a full service making sure I checked the spark etc and everything seemed ok.



    After the service it run really well and I've done several rides since lasting up to an hour each and they all went well.



    This week I went out for a longer ride and after 90 mins the problem came back. It struggles to rev under load, mainly between idle and 5k rpm and then slightly better above this.



    I can let the bike go cold and try again and the problem is still there.



    My first thought was an issue with the carbs but in all honestly I don't really know.



    Any help would be much appreciated.



    Ps. To top it off, the ignition switch also failed on the last ride so I had to do a temp fix to bypass the ignition switch.
     
  2. ridervfr

    ridervfr Member

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    Charging system? What does it charge at during idle<>? then rev it to 5000 RPM and see what the voltage is. Did you ever change the regulator/rectifier on this bike? How where the plugs when you pulled them? Did you check for spark>?

    Whats the mileage on the bike? Ignition switch failed? So what was the bypass? Jumping starter solenoid with a screwdriver? Let us know.
     
  3. R89B

    R89B New Member

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    Hi. Thanks for the reply.

    I haven't check the regulator but know it was replaced about 10 years ago by the previous owner.

    The old plugs looked ok and when I checked the spark during the service they all seemed the same.

    After we narrowed down the fault to the ignition switch at the road side, we effectively cut two of the wires to the ignition barrel and joined them together, just so I could get home.

    I've pulled the battery from the bike now as I can't turn off the ignition.

    I will dig out my multi meter (if that's what it's called) and check the charging rates.
     
  4. Diving Pete

    Diving Pete Insider

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    could be ht leads or coils breaking down - do you know what cylinder / s are affected?
     
  5. jethro

    jethro New Member

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    What happened to all the previous replies to this thread?
     
  6. R89B

    R89B New Member

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    Hi. I've not seen any other replies myself so I'm not sure.
     
  7. jethro

    jethro New Member

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    I had replied previously as well as several others and it's almost like a new thread now.
     
  8. R89B

    R89B New Member

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    Hi all. I've only just had a chance to look at the bike and after working through the flow chart in the Honda service manual we diagnosed it to the Spark Plug caps. The coils etc all seem to be operating correctly but the rear 2 plug caps failed the resistance test with nothing passing through.



    I've just ordered 4 new caps and will also replace the leads. Fingers crossed.



    Thanks for all your help.
     
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