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Carby trouble - 4 cylinder motor

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by toughguy, Apr 4, 2005.

  1. I recently purchased a Yam YZX 250 (Zeal). I'm really enjoying the bike but have a problem with carburation (I think?).

    When the bike is cold, it runs like a dream wiith smooth power all through the rev range.

    Then, when the engine warms up, it doesn't run well between 2000 and 6000 revs. Response is very poor and it doesn't get going until I pass the 6000 rpm mark.

    I serviced the bike when I got it 2 weeks ago, plugs, air and fuel filter, oil change, & drained float bowls.

    Any suggestions? My gut feeling is that it's a carby problem but not sure.

    Is there a chance that imported bikes such as this are not jetted for the Australian Climate? I'm in Perth.

    Appreciate your help peeps.


  2. have you tried different fuels? and has it always run like this since you got it? i had similar issues with my bandit when i used crappy fuels, always sorted itself out when i switched back to mobil 8000 or BP ultimate. its also possible that you've got electrical issues, did you set the spark plug gaps properly? and how hot is the motor getting? if it is overheating, then you might run into issues like that, then if you fix the overheating, the performance should straighten itself out aswell.....
  3. You serviced it 2 weeks ago?
    The bike is now running like a bag of shit?
  4. thanks

    You know what? I was actually thinking exactly that on the way home. I may have put ordinary 95 octane into it. I will take your advice. Hope thats all it is. Didn't check the spark plug gaps. Will try that if petrol doesn't sort it.

    Thanks again,


  5. It's resolved!!!

    Thanks for the help guys. I took the bike apart this evening and figured out what was wrong...

    The slide in Carb No 3 was stuck in the open position. Now this was fine when the bike was warming up cos it ran one cylinder rich. But when the bike got up to temperature, the open slide was choking cylinder No 3 with fuel (but no air) at low revs when the butterfly was closed. Of course, when I wacked it open, it cleared itself and ran smoothly again. (above 6000 RPM)

    It took me 3 hours to sort the problem out. I've no idea why the slide was sticking. I used emery paper to sand it down and try and remove any edges.

    I'm now enjoying a beer while writing this. (still stinking of petrol)

    Thanks again folks.