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CBF250 idle problems

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Traviss, Sep 22, 2010.

  1. Have a mates cbf250 with an Idle problem..It over rev's once its been ridden tuned the carby at running temp ,ride it and the revs pick up again adjust and then it drops to low ,turn off for 5 minutes and start idle way to low..
    Could it need valve clearance check next or do you think its small vaccum Diaphram on the rh side (300 dollars from Honda)
    Carby has been stripped and cleaned the only small problem is this small diphram seems a little streached bowl was clean jets clear ..Tank has been cleaned and fuel replaced ..
    All cables are fine and the throttle control returns to idle set ..
    This bike has done 10000km but has sat for 9mths..
    Any ideas..

  2. CBF's wont run or run like shit if their valves aren't checked at every service. Read more here
  3. cbf is a good name for those bikes regarding honda's attitude to them
  4. There used to be an aircraft parked at Moorabbin Airport with the registration letters 'CBF'. Rather appropriate as it hated starting first thing in the morning !
  5. Sounds like valve clearances are out. It's quite an expensive job as well from what I hear.. $400+ seems to be the going rate with a normal service. I think these and VTR's need to be checked at the initial 1,000km service. Do you know if they did that? If they didn't they were probably out a bit and it's just got worse over time.
  6. You have a vacuum leak to the fuel tap. As it heats up it leaks and allows the tap to close. This in turn leans out the mixture and the revs rise.

    Replace the vacuum hose and make sure all fuel and vacuum hoses have good connections.

    Also check the tank vent. That could be making it lean.
  7. No Vacuum pipe to the tap..I think it might be a vacuum prob..
    It only has 2 vacuum hoses to the carb ,one to the small diaphram on the side and one to the inlet manifold this has a t junction that goes to a (looks like ) a solenoid valve .
    The shimes shouldnt be worn enough to cause the problem but I will check them anyway..
    The chocked worked after clean and the idle was fine..Rode it and it jumped to 3-4k this morning the chock wouldnt work and he had to hold the throttle part open to get it to run ..
    Fuel was replaced, tank cleaned ,tap cleaned and filter..
  8. REally? hmmm

    Still double check your fuel line connections and blow out the tank vent again. It definitely reads like a leaning problem.

    Cab boots to the heads? Spray some carb cleaner around them when the engine is running.
  9. Def only has a fuel hose to the tap no vacuum hose or anywhere for it to connect to the tap..
    The tank breather is fine ..
    The spark plug looks like its running a little too hot ..
    I will give it another look over on sunday and see if any hoses are cracked or the inlet manifold is leaking..
  10. more supporting evidence for leaning mixture.