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Occasional klank sound when starting engine -- CBR250RR

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by mugen86, Apr 17, 2008.

  1. Ok I'm in neutral, my kick stand is up and i press the starter... and suddenly I hear a slight klank noise coming from the engine and the starter doesnt start the engine.

    This has happened to me once when the engine was fully warmed up after a 30-40 minute break and once when the engine was cold -- after around 5-6 sitting outside in cold weather. In cold weather it was impossible to start after the klank sound... i held the start button but the engine would not turn over. I applied full choke for about 5-10 seconds and a tiny bit of throttle and only then would it turn over. When the engine was already warm... I had to press start a few times and apply a bit of throttle for the engine to turn over. Usually when its warm it turns over right away and when its cold it takes 2-3 tries at the start + throttle blip.

    I have done 70kms on the bike over the last 5 days and this has happened to me twice. Has anybody else experienced this problem? thanks
  2.  Top
  3. a klingon?
  4. i agree with th above comment... same thing with my 250 and dat was the solution
  5. Wow thanks for the quick response... mmm but if there was water in the engine wouldnt it be noticeable while driving? I am still able to start the bike.

    a coolant, oil or fuel leak also seem to be common causes of Hydrolock, but wouldnt a leak in either of the three be easily noticeable?.
  6. I am familiar with the "Klack" sound. (Bit like 10,000 men saying "WOP" at the same time, ah forget it)


    I do have that sound, occasionally when i start the bike. Explaination sounds fair. I know my fuel tap leaks a tiny bit. Wouldn't have though it an issue, how can fuel flood the cylinders from a leaking fuel tap? How can it flow past the fuel pump through the jets and fill the cylinders.
  7. Whats the difference between a BattleStar Gallactica and Toilet Paper ..?????


    They both hang UrAnus looking for Kling ons ...

  8. There is no fuel pump - it is gravity-fed.

    Fuel will easily flow past jets at atmospheric pressure - the holes are plenty big enough.

    The fuel overflows the carb needle jet and keeps looking for the lowest point of exit, straight into the manifold and into an inlet port, and then through an open or slightly worn inlet valve into the cylinder.

    I'm not saying the OP has a hydraulic lock, just saying what happens for it to occur.


    Trevor G
  9. But, wouldn't (or shouldn't) the carbie floats raise and press the block valve, shutting down the fuel entry? Or does a vacume pump not have carbie floats and relies on the other functions of the bike to regulate the flow?
  10. The needle valve can be worn, or the float not correctly adjusted. Also old O-rings cause them to leak.
  11. Do you mean that the engine starts to turn over ( the "rarr rarr" sound of the starter motor in action) but then stops very quickly with a "clank" sound?

    "Turn over" is not the same as "start" - I just wanna make sure we are on the same page...

    When you held the starter button did you have silence, or was the starter working (the "rarr rarr" sound) with the engine turning over, but not "firing" into life?

    If it is hydraulic lock (fuel leaking into the cylinder) then it would run very roughly at first, even when cold, because it is far too rich a mixture at first. I guess that could be why you had to blip it to get it going...or keep it going.

    A hydraulic lock can be partial, so that after several attempts (not really advisable, though) enough of the fuel will be dissiapted to allow the engine to turn over again. It is a very dangerous situation in that the average starter motor develops enough torque to force the pistom up against the incompressible fuel trapped in the cylinder with such force that the conrod is bent when it stops suddenly.

    You will only know what it is by:

    1)a Removing the fuel line to see if fuel is running out when the tap is turned off or

    1)b Removing the fuel line to see if fuel runs out when the bike is not running, if the tap is vacuum operated

    2) If it is a vacuum operated tap (there will be a diaphragm enclosure on the tap body, and a vacuum line from the inlet manifold to this diaphragm body/assembly) there is also a possibility that the vacuum diaphragm is damaged and the tap is passing fuel directly into the manifold via this line.

    I can give details on tracking this down once you determine what sort of tap and "off" system it has.

    3) Removing a sparkplug or two (all of them, probably) when the "clank" occurs - then see if the engine will turn over on the starter motor. If it does, and there is/was a hydraulic lock, fuel will spurt out of one or more of the plug holes, and one or more of the spark plugs will be wet.

    Let's know how you go.

    Trevor G
  12. Yep. Correct, that is exactly what should happen.

    As etelmo has pointed out, gummy or dirty or worn needle and seats will sometimes allow fuel to continue to flow in.

    And as I said earlier, on some occasions fuel is able to enter the cylinder via the inlet manifold, via the vacuum feed to the tap when the diaphragm fails or the tap is leaky and the diaphragm fails.

    Just the tap is vacuum operated, so that fuel should only flow when the bike is running.

    The vacuum operation of carburettors is different in that the throttle slides only lift when there is enough engine vacuum to lift them. This is also designed so that if the engine is running very slowly and the rider cracks the throttle wide open, the slides will only lift far enough to allow the correct amount of fuel/air to enter. Theoretically it prevents the engine "bogging" if the throttle is opened too far too quickly.

    All the best