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Choke

Discussion in 'Bling and Appearance' at netrider.net.au started by cakeman, Apr 15, 2009.

  1. Hi guys, this is a puzzling me a little and it is a very straight forward question.



    I was under the impression when you pull the choke out it REVS the engine more (more fuel or air... i forgot which one).

    When i pull mine out all the way, the bike stalls. Ive been trying to set my idle speed and thought it best to do it with a warm engine and no choke at all. When i pull it out completly the engine stalls... i thought it should have been the other way around, when you pull it out completely the revs get higher.

    thanks in advance
     
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  2. The choke is a device which actually increases the fuel in the air:fuel ratio.

    At times this will increase the revs. It is used when the engine is cold to change the mixture to run sufficiently when out of it's normal heat range. But when the engine is up to operating temperature, using the choke changes the air:fuel mixture out of it's optimum range and can cause the bike to run badly/flat or stall.

    Whereas the idler adjuster controls how low the default (throttle "closed") position is on the carby. Basically it does not allow the throttle to close completely, but hold's it open a fraction to allow the engine to idle.

    What bike are you doing it on - the one in your sig?

    Edit: added a bit of detail.
     
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  3. Only use the choke when starting the bike.
     
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  4. Or to do a fuel dump, when you have soiled your needle and seat.
     
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  5. Thanks, Yes im doing it on a RVF400.

    I was going to adjust the idle by having the choke completly off when the bike is at operating temp and set it for around 1300rpm. However when i pull the choke out all the way the bike stalls.

    Im wondering if the choke is on when its pulled out. I thought when the choke was out, the choke was on, increasing the AFR. However it doesnt seem so.

    Is my logic right in regards to setting the idle? Choke off when engine is at operational temp and then set the idle for 1300 rpm?
     
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  6. choke pulled out = choke on
    choke pushed in = choke off

    A choke pulled out will make your bike stall, eventually.
     
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  7. Thanks, Yes im doing it on a RVF400.

    I was going to adjust the idle by having the choke completly off when the bike is at operating temp


    Yep

    and set it for around 1300rpm.

    Yes, keep the choke off and use the idler adjuster screw to set the revs to the correct ilde

    However when i pull the choke out all the way the bike stalls.

    I'm not surprised - don't do this step! See my original reply (and Loz's) - don't use choke when engine warm or it'll fcuk with your AFR. You only wanna change your AFR when the engine is cold to compensate - ie only use your choke when engine is cold.

    Im wondering if the choke is on when its pulled out. I thought when the choke was out, the choke was on, increasing the AFR. However it doesnt seem so.

    Choke out = on, which increases the FUEL in the air:fuel ratio (ie to be pedantic it reduces the AFR) ...but only something you need to do when engine is cold.

    Is my logic right in regards to setting the idle? Choke off when engine is at operational temp and then set the idle for 1300 rpm?

    Well the logic is mostly right in that you keep the choke off at operating temp, but when setting the idle speed I suspect you are using the choke instead of the idler adjuster screw.

    Does this make sense?

    edit: :woot: 1000 posts :LOL:
     
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  8. I'm confused. Joel's right.

    If it's stalling with the choke off (when the bike is warm) then the idle needs to be set higher.

    Also 1300 seems a bit low to me for that bike. Someone heare will be able to confirm that.
     
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  9. Thanks for all your help i really do appreciate it all.
    Im a pretty slow learner and a little confused with this bit:

    If the Choke is Pulled out all the way and is ON at operating temp, why does it stall? I thought it would increase the revs even more?

    When it is cold and i pull it out, it stalls as well. when i push it in, revs seems to increase
     
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  10. Not that confusing.

    I believe he is trying to use his choke to set his idle speed. He needs to find the idle adjuster screw and set his idle speed with that.
     
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  11. A little confused here ...
    If engine is stalling when applying choke on a warm engine.. DONT use choke. It should only be used on a cold engine.

    IF you are having trouble with the engine stalling on cold startup after applying choke, try this:
    Start engine .. NO CHOKE, then gently apply throttle ( bring the revs up ) as you apply choke. Sometimes using choke at idle can lead to unburnt fuel fouling plugs, reving up can assist in dumping the excess and allowing the plugs to play catch-up.

    PS: if a warm engine won't idle without choke, then you may have other problems such as a vacuum leak making the engine run too lean.
     
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  12. Think of a choke not as a 'rev-raiser' but as an 'air to fuel ratio changer'. Sometimes it helps running, sometimes it prevents the engine running.

    It normally helps running when cold, hinders it when at operating temp.

    It sounds like the bike either needs a tune, or does not need any or very much choke in order to start when cold.
     
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  13. thanks again guys for all your help, really appreciate it.
    It most probably needs a tune. Thats out of my league so ill take it somewhere soon.
     
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  14. I just tried this and it worked a treat! Thanks.

    Does this mean spark plugs may be due for replacement?

    I tried in vain to get the plugs out but no luck. I have a 16mm and 21mm spark plug socket but didnt seem to work. Ive just read that the rvf400 needs uses 8mm spark plugs so i need to find a spanner with 8mm plug. THAT SHOULD BE REAAAAL EASY! :)
     
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  15. Happy to have helped :)
    Plugs should be accessible with a 5/8 plug socket.
    Changing the plugs, may not help, but wont hurt.
    My old 250 hornet did not like choke unless I applied it they way I described. Plugs were ok, fuel mixtures fine. Some engines are a little temperamental I guess.
     
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  16. Changing the plugs wont hurt and it may solve the problem. So that first. You may need an 18mm plug socket. Many bikes use this and they are not that easy to find.

    If the plug change doesn't work, I'd be guessing it is running too rich on the idle jets/screw.
     
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  17. Apparently its a 13mm socket i need for these 8mm plugs.

    I had a feeling it was running a bit rich.. it does need a tune and to be leaned out
     
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  18. When your engine is cold, it needs more fuel to run... hence pulling the choke on makes it run.

    When your engine is warm, it needs less fuel to run. Hence you turn the choke off.


    When you pull on the choke when the bike is warm and running, you will put too much fuel into the engine, flood it and it will die. This is because there is too much fuel and not enough air in the engine.

    Your logic of choke = higher revs wouldn't work because you need air to burn that extra fuel that the choke throws in there.. This is why people put superchargers and turbos on their engines. They push in more air into the engine, and they adjust their fuel intake to also be higher so they get a bigger explosion in the engine which = higher revs and more torque.

    I hope that clarified the workings of an engine a little better.

    Basically more fuel and not more air = bad.
    more fuel and more air = good

    choke = more fuel only. bike = stall.
     
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  19. Just so I don't start a new thread, I've got the same problem.

    When cold, I used to pull the choke out to about 3/4 and start it and adjust it back so that it wasn't revving too high. Usually after about 1 minute I'd have no choke and it'd be idling fine. Nowadays, if I pull out the choke at all when starting up cold it just won't start up. If I start it with a little throttle then try and give it any choke, it stalls. I've been starting it fine and letting it warm up without any choke but my issue is that it should work correctly. I'd never have thought that the carbs on a new bike would be more temperamental than the old Stromberg was on my first car (which never let me down)!

    This issue started before my first service so it wasn't the fault of PS.

    Any hints or should I wait and bring it up at my next service considering it starts first time every time and only needs minor throttle for about 5 seconds before I can leave it to sit there to warm up?
     
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  20. It is your carbs running too rich, I presume. This happens.
    If it is painful enough, get someone to tinker with the carbs to sort it out, otherwise, get it done at the next service.
    Remember, that your bike is pretty new, and the characteristics of your engine are still maturing - so to speak.
     
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