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Engine Cuts Out At 100km/h+

Discussion in 'Technical and Troubleshooting Torque' started by MowgliB, Nov 15, 2012.

  1. Hi guys,

    I have recently uncovered a very troublesome issue with my '95 CB400.

    When riding on the freeway and get over 100km/h, after about 2 minutes at that speed then engine just cuts out. I figured it was some sort of electrical fault. I have gone through and cleaned all of the contacts on the rectifier and the fuses. Checked the rectifier is functional. I have even taken a ride down the freeway with a voltmeter taped to my fuel tank.

    It seemed to me that the battery was still being charged by the alternator even when and after the engine cut out. (The voltage remained at 13.8V both before and after engine failure)

    So now I am back to the drawing board.

    Does anyone have any other possible causes for my bike only dropping out at 100+?


  2. Faulty sensor for the rev limiter maybe?
    Wild guess
  3. Prewash spray ... gets skid marks out ... usually
  4. Is it fuel injected? if so it could be the throttle position sensor. I had a faulty wire on mine and it would cut out and lurch at 100 kmh. That or a faulty kill switch.
    When you describe it as cutting out do you mean completely or does it act like you are turning off and on the kill switch?
    Vibrations at that speed can cause a faulty electrical system to go mental.
  5. If you ride at a slower speed in a lower gear to simulate highway revs does it cut out?
    • Like Like x 3
  6. Check the tank breather hole and/or hose for kinks, you may just be getting vapor lock.
    • Like Like x 1
  7. have you got petrol in the tank ?
  8. fuel filter is a possibility
  9. If it just cuts straight, I think your guess of electrics is accurate. Being a honda, doubly so.
    • Like Like x 1
  10. #10 MowgliB, Nov 16, 2012
    Last edited: Nov 16, 2012
    More info: Specifically at Phil01. Forgot to mention this in the original post. When the engine cuts out, once I drop back under about 90km/h the engine will kick back in. (key information, I know)

    smee - Would a '95 CB400 have a rev limiter? I have a workshop manual (some dodgy translation from Russia) and there appears to be nothing in that. Would they fit one for compliance here? It is not fuel injected. You are right though, it does act pretty much like I have tripped the kill switch. That is definitely some food for thought. It only happens at 100+, if it was a loose connection, surely it would happen at random speeds in random intervals?

    Superunknown - Being in Melbourne City, I am not game to ride around the busy streets at high revs to find out. If it did cut out the resistance in the engine might slow me down so fast someone hits me from behind. When I get a chance to go somewhere quieter I will definitely be giving this a test, however.

    VTRAffair - I will have to give it a once over and have a look, would it be likely though that it would come back on a lower speeds in this case, though?

    phil01 - Same question as VTRAffair.

    Thanks for your bloody quick responses! Amazing.


  11. well the only thing changing at that speed is wheel
    speed ,
    atm im NFI

    its a clean cut right ? no splutter at all ?
  12. would under load be consistant ?
  13. There was an issue with hose routing on some VTR's that meant at certain speeds, forward air pressure was negating the vacuum line attached to the fuel tap and the diaphram would close off, cutting fuel supply. They fixed it by fitting a plastic sleeve around the fuel tap on later models and the issue went away.
  14. vibrations at 100 kmh are obviously causing some electrical issue. IT could be a dodgy kill switch connection. a dodgy sidestand connection, a dodgy clutch lever connection, all these can kill an engine if the bike is carbied. As for rev limiters well again that was a wild guess.
  15. Pretty simple electrics on that model Smee, Kill switch is a possibility, No side stand switch as far as I can see from the Wiring Diagram. The clutch switch doesn't affect the run circuitry only prevents you from cranking. Rev limiter is built into the CDI so if it is possible but unlikely.

    Wiring Diagram

    If it is electric then a more obscure but engine speed related problem can be cracks in the High voltage circuit causing flash over, HT leads, Spark Plugs Coils or as a last resort the CDI,

    Lilley's point is an important one though is it a sudden cut out and sudden return of does it cough and splutter?
    • Like Like x 1
  16. well rev limiter is unlikely unless he accelerates like a um a "insert somthing here".
    what a pain in the arse symptom - only at 100k , but yer as smee said has to be
    vibration related , unless he is not describing the cutout properly - it would be
    nice to get a confirmation of a clean cut out to eliminate fuel supply, even if it is
    unlikely its still a basic ( fuel air compression spark) and needs properly eliminating.- ignition lead is a possibility, faulty terminal etc as it will still be firing etc so is high up there .. rambling now soz.
    heck just fix the vibration and get he wheels balanced lol
  17. Cheers guys I'm not really aufait with the electrics of that model but the vibration theory at that speed is a cause for concern
  18. Had a bike once which did the exact same thing. Turned out to be the clutch lever/mirror mount assembly shorting out the kill switch wire. The mount clamp bolt was loose allowing the assembly to pivot a little on the bars. When you got up to speed, wind pressure on the mirror caused the assembly to pivot rearwards on the bars, and this movement had worn throught the insulation of the kill switch wires & eventually started to short them out .
    Had another bike do a similar thing. This one turned out to be a faulti CDI box. When you rode the bike sedately, everything was fine. But when you rode it hard for 10 minutes it would then cut out, but would not run again for an hour or so.
    Also another similar situation on another bike ended up being the pulser/pickup coil. Would run for 10min then cut out for a few minutes, then youd be off running again.

    One quick way to test if it's spark related is to buy an illuminated plug cap, which lights up every time the spark plug fires. Ride the bike with one of these & you can see straight away when your bike cuts out if it's still sparking or not.
  19. +1 VTR Affair, sounds to me like its starving for fuel due to blocked vent, filter or kinked hose. Is it carb or FI?