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Stalling instead of idling :S

Discussion in 'Technical and Troubleshooting Torque' started by TOMatoPASTE, Apr 25, 2008.

  1. Ok, I'v got a very annoying problem with my zxr250 at the moment. Ran it to reserve the other day and, after the usual mucking around trying to get it started again on reserve tank (not exactly up to modern standards lol) and then refuelling....it wont idle.
    If i let go of the throttle it simply plumets in the revs until it stalls so i have to go around riding everywhere and setting idle speed manually with the throttle(not fun). Now iv done the obvious and fiddled with the idle speed nob thingy and that now seems to be doing sweet **** all and the only way to get it to idle is with the choke on.
    My assumption would be either broken idle speed adjuster cable or problem with air fuel mix somewhere along the line but really have no idea. Any ideas, suggestions, explanations would be greatly appreciated :)

  2. How far did you run it down on reserve, and had you let the tank get that empty before?
    Sounds likely there could have been some rust or other crap in the bottom of the tank which is now clogging up the pilot jets and starving the engine for fuel at low revs (which is why pulling the choke on fixes it).
    I'd start out by draining the float bowls of the carbs and checking the fuel that comes out.
  3. As jd suggested "drain carb floats"!
    i would also suggest if you have an air compressor handy, to blow through the jets with the float bowls off, sounds like you have picked up some debris in the jets from the bottom of the tank!
    Look and Look very closely at the jets for signs of small bedris and if you are tempted to prod, please do it with a tooth pick, you will not damage the jets but be very carefull!!

    I would also check you vacuum lines and check for perishing of the pipework, as air leaks will cause the same problem, you may be running down the wrong avenue!

    Hope it helps
  4. Thanks for the advice people! Umm not very low at all. i ran out across the road from a servo haha and yeh its been run down to there and lower a few times before without any troubles.....mmm in any case sounds like its probly a job over my head at the mo. Thanks
  5. 1. idle jet/s in carb blocked up
    2. idle adjuster cable fallen out (this is my guess cause on 4cyl means you'll need to block up at least 2-3 of the idle jets before it can't idle and you'd notice a loss of power at low revs (below 5k or something~)

    both require you to take the fuel tank off and take the carbies out, not a hard job but if you havn't done it before best to get someone who has to help you out
  6. I wonder just where petrol flows from, when it goes from the tank to the carbs.

    Does it flow from the top of the tank?

    Or does it flow from the bottom of the tank.

    If it flows from the bottom of the tank (which is what seems to me to be the case), do you mind explaining what effect occurs with a nearly empty tank, to allow any more muck through, than with a full one?


    Trevor G

    PS And if you say it happens when he switches to reserve, we would have to ask if he ever did that before, too...and it seems he has.

  7. Are you absolutely sure you were adjusting the idle speed control?

    It usually is a plastic-headed (knurled) knob near or at the side of one of the carbs. It usaully is not a cable operated device.

    The idle speed adjuster usually has enough adjustment to make it idle even if the pilot jets are blocked...usually.

    As jd has suggested it could be a problem with bad fuel, and you could have a hole in the strainer around the reserve entry for the fuel tap which has let muck get through when you turned to reserve.

    It's really easy to check - at the bottom of the carb float bowls are drain screws, one for each carb. These are usually connected to drain hoses which exit under the machine.


    The best pic I have is of a VTR250 Honda - the bottom of your carbs will be similar. You might not be able to get to them as easily, though. ;-)

    Loosen the screws a turn or two (no need to pull them all the way out) and drain the fuel into a clean container. If the fuel is mucky, as long as the muck didn't come from the end of the drain tubes, then you probably have blocked pilot jets.

    Don't touch the brass coloured screws - you do not have a need to adjust the mixture before you solve the blockage.

    If there is water or some other foreign and undesirable liquid in there, this will appear as something not unlike a bubble in the petrol. Rust will appear as...yup, you guesed it, rust. Those little specks can block a pilot jet in no time flat.

    And I will owe jd an apolgy of sorts... ;-)

    All the best

    Trevor G

    PS It doesn't have to be rust - any small particles of muck can block a pilot jet.
  8. im gunna have to agree with chris's idea of the busted cable as the bike runs smoothly and powerfully as normal. its just idling that has the issue.

    i think the point with the rust/much from the bottom of the tank is that the normal/'on' fuel line takes fuel from a position part way up the tank and it is once the level drops below this that you 'hit reserve' and need to change to the reserve line which feeds from the bottom of the tank.

    and this problem isnt just when on reserve just in case that wasnt evident in my first post. it occured when i had to change to reserve but has persisted since

    yes im 100% sure it was the idle speed. i regularly adjust this and now it isnt working which suggests the cable is broken.

    once again, thanks for all your detailed responses. i might try out testin the carbs etc before taking it to a shop (atleast taking the fairings off will reduce labour :)
  9. Neither, it normally flows from an inch or so above the bottom of the tank. It only flows from the bottom when the tap's set to reserve (hence the initial question).
    And when it does start to flow from the bottom the fact that little fuel is remaining means that the concentration of crud in the fuel reaching the carbs is much higher, increasing the chances of something clogging.
    Of course I suspect you already knew that and were just trying to be smart so the above is really for those not familiar with how it all works :).

    Does sound like it could be an issue with the idle speed adjuster - of course all that does is adjust where the throttle cable snaps back to when closed. If the adjuster is still working then you should be able to see the cable move slightly, or if you have a good sense of "feel" have someone adjust the idle speed with the engine off whilst holding the throttle (apply a tiny bit of pressure to take up the slack in the cable and you should be able to notice it either tension up or slacken off when the idle speed is adjusted).
  10. This is way easier then clearing out the jets in the carbs cause alot of the time you don't have to take the carbs out if you have small hands.

    The end of the cable where it attaches to the throttle cable at the carb area will probably just have unscrewed itself.

    All you need to do is take the fuel tank off and maybe a side and/or front fairing. (easy for a beginner, just be mindful of where the fuel tubes go when disconnecting them)

    Just by looking around you should be able to see the problem.
  11. Actually, it wouldn't matter how much fuel is in the tank - even if it is full.

    When you switch to reserve, if the strainer is broken (not unusual) or there is muck there, it will run in just as readily, maybe even more readily, with a full tank as with an empty one.

    It's not a case of concentration as much as opportunity.

    A carb drain at this point, into a clean, empty container, will show more than it will hide about the problem and its solution.

    Sometimes draining the carbs will solve, in itself, that bad idle problem, if it really is due to muck (water, liquid or solid matter) in the fuel. All the OP needs is a long handled, flat blade screwdriver, I reckon, and an old icecream or margarine cointainer, or similar. ;-)