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Rough Idle at start

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  • Rough Idle at start

    Hey guys

    Got a new bike. Its a 2008 Kawasaki Ninja 250r in that sexy sexy blue I managed to get it for 3500 with 10,000 on it because the PO hadnt taken good care of it (not serviced in the 2 years/5000 k's he had it.

    After some basic servicing it runs great other than that it needs choke to start at all times other than like high 20's+ weather. It's not an idle screw issue as once it is warm it idles fine, possibly slightly high at 1400 rpm ish. When I start it in any weather below 25 it struggles at 900 ish rpm's and then dies if I don't use any choke.

    Anyone got any ideas on what it might be and how to fix it? my guess would be that knowing how badly the previous owner kept it that he left fuel in it ages and the carbs have gummed up with stale fuel a little bit.
    Attached Files

  • #2
    Is this bike injected? I noticed you mentioned a choke? If it is carburetor operated you may just need to let it warm up for about five or so minutes just to let the bike warm up. I had to do that with the cbr 250rr I use to ride. It hated me if I didn't give it time to warm up and would miss fire and stall on me if I didn't do so.
    If it is injected, 2008 I would have expected it to be injected, you may need to get the ecu re flashed.or get the bike looked at by a good mechanic.
    Evil mechanics murdered my car. So I resurrected it back from the dead.


    • #3
      250R, EX250, carb'd.

      To be honest, for the most part, what you've described is exactly how it SHOULD behave.

      The choke is there specifically for cold starts. Having to use it before the bike warms up is normal. That's why it exists. Not needing the choke in warm/hot weather is normal (even then it's still a 'cold start'). The engine stalling by cutting the choke before the engine is warmed up is normal. ~1400rpm idle (warm) is normal (though if it's stable a little lower, that's fine too). All of it, normal.

      The instruction manual will say all this - atleast the one for my bike did.

      Kawasaki also recommend, atleast for the older ZZR250 / GPX250, not to let the bike sit idle to warm up - they say its better to ride it to warm it up. So start it, hop on and ride away, after a couple of minutes you should be fine to cut the choke. Don't flog the guts out of it, ride gently, but yeah, just ride it.

      Personally I sometimes cut the choke as soon as I start riding. Also, I sometimes had starting issues, but found them to occur if I had throttle on startup, it actually started easier with the choke on and no throttle applied (different but maybe related anyway).

      If the idle is rough with the choke on, tricky one, maybe check the choke cable, or perhaps the carbs need a service/clean.

      I find the choke can be quite sensitive. Lots of the lever movement does nothing, then it kicks in. And if its turned on too far, can make it run too rich - so it's better to back it off at that point. Either way, even just leaning on the lever (without the feeling of even moving it) can be enough to adjust the idle.
      Last edited by Rake; 20-10-2012, 11:36 PM.


      • #4
        Thanks for your input guys. Seemed a bit odd to me that it needs choke in anything under 20 degrees but if there's nothing to be concerned about I might just leave it be.


        • #5
          Sounds completely normal to me. As Rake said, the choke is designed for cold starts. If you don't need the choke on a cold start (cold temperature), you're running too rich and you'll foul your plugs.

          If your idle is stable, it's fine. If however it's a bit twitchy and sporadic, could mean either you need to open up the carbs and clean them; should do this anyway considering it's basic and you said the guy didn't look after it very well to begin with, or maybe the carbs are out of balance. Being a 2 cylinder, it won't be too hard to balance but you'll need either a DIY made manometer or a store bought one. DIY one is more accurate so I've heard although absolute balance is near impossible to achieve, even for the pros. This device connects to your vacuum ports, and with the bike running, you use it to measure vac pressure and balance them. Otherwise a mechanic charges around the $150-$200 mark for carb work.

          If neither of these sort your problem, could be a dud float or something like that. Cleaning and balancing should resolve any unstableness though.

          But as has been said before, it's normal for you to need choke on a cold start, and can be bad if you don't.
          My Ride:
          2004 Holden VYII Berlina

          My Other Rides:
          1992 Honda CBR250RR
          2006 DRZ400SM