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Hard to start when HOT.

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

  1. Ok mine starts fine when cold, but very hard to start when warm.

    In fact its almost impossible to start when its warm.

    It winds over and winds over, and after a LOT of winds, it starts to gently sputter, then clutter, then flutter!, then START!!. When it starts the idle is VERY slow, and slowly starts to increase by itselft and eventually stops at about 2000.

    Most of the time the battery will start to chug before it gets a chance to start.



    And its pissing me off because im a mechanic on cars and its quad carby and i havent worked on many carbies blah blah.

    But yeah its a quad carby Kawasaki ZXR250r 1990 model.




    Starts fine cold

    Choke very sensitive

    Almost impossible to start when warm.

    Idle is very unstable when cold (2000 one second then goes up to 6000 and sits there, etc)

    pls help.

    *Dont say battery cos its brand new and it cranks really fast.
     
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  2. Hey, i am no expert on this either but it does sound like your bike is running a fair bit lean. The heat causes the bike to lean out. Might wanna go and check your spark plugs and see what colour, white= too lean... Hope this helps a bit :)
     
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  3. choke is stuck
     
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  4. Mine likes a tiny bit of throttle when hot, just enough to lift it from idle.
     
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  5. Couple of possibilities relevant to an oldish bike.

    Carb intake rubbers probably look like a fossilised elephant's scrotum after 18 years. Could be hardened, cracked and leaking.

    Difficult hot starting can be a sign of poor compression due to engine wear. The bike's 18 years old but you don't say what kms. Might be worth doing a compression test.

    Don't let multi carbs put you off. They're only one fairly simple carby multiplied by four. The only real complications are balancing 'em (not that hard) and paying for four of everything when you rebuild them (really really hard, particulaly at the Big K's spares prices.
     
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  6. yeah 65,000kms it could be engine wear i guess.

    i was trying to tell myself it wasnt that because i dont want to have to rebuild it :)

    Thing is it revs very cleanly, and has plenty of power, doesnt blow any smoke, and "sounds" like it has plenty of compression when it winds over.
    But yes its a possibility.
     
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  7. I've heard of that problem. Apparently its due to the idle being set too rich.
    Bike starts fine cold without any or very little choke and is easy to flood.

    When the engine's warm, it takes a few turns longer as its too rich.
     
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  8. I could agree with theory, cos it does smell rich when it eventually starts.
     
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  9. Its your Torque/Rev Knob (Not Choke) Or Also Called Idle Pin, its set too high, Turn it down.
     
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  10. The engine revving up when cold is classic 90's Kawasaki. They all rev their tits off when cold. Balance the revs and choke as well as you can and ride off as soon as the engine will let you.

    Your hot starting problem might be fuel vapourisation ~ the fuel in the floats boils off due to the heat from the engine, not helped by relatively small floats on the carbs. You then have to suck through more fuel by turning the engine over on the starter as the vacuum tap prevents fuel flowing by gravity.

    Try turning the tap to PRI for a minute before restarting. Don't forget to switch back to ON when it fires up! Good luck.
     
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  11. this would be my guess. or stuck choke.

    Get the carbies cleaned and balanced and then if it's still doing it look at leaning out the idle mixture.
     
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  12. This guy was right.

    I normally turn it up when its cold, cos it wont idle. Then i ride around and often when i stop the idle is at 4k or something. Then i turn it down. SO it starts fine now. But before i wasnt turning it down.

    Its starting a lot better now.
     
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  13. Maybe i was imagining it, because its really hard to start again now.

    I guess i should pull it apart again and have a look. Im sick of pulling it apart it will be like the 7th time in a month i have had the bike apart ><

    How do i tell if the choke is stuck on?Its got a sliding rail that pulls out a little plunger, it pulls the same plunger on all 4 carbies at the same time. And seems to push them back in when released. But could it still be stuck inside?
     
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  14. Check the cable. Choke cables tend to seize sometimes.

    I've been told you shouldn't adjust the idle screw, instead just use the choke when its cold. Thats what its there for. Idle is supposed to be set for when bike is warm.
     
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