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Fuel mist spraying out of carby trumpets when revs pass 8k!

Discussion in 'Yamaha 250cc In-Line 4's' started by guestxc, Mar 30, 2009.

  1. guestxc

    guestxc New Member

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    I'm back with yet another delectable problem! (...yes i hear the audible groan <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->)

    SO what's happened (before I start yes i searched. I am still confused):

    Symptom 1: My bike refuses to rev past 8-10k rpm, hot or cold.I read some things about jets and the like, but I've always known EFI way (I was into cars before bikes) more than carby's so not too confident there but will pull them out if I have to.

    Symptom 2: When throttle opened (with bike warm)a decent amount fuel sprays (like a mist out of spray bottle) out of the carby trumpets. Not one or two but all four of them spit fuel out of their intakes! Airbox is off.

    I have tried:
    New fuel (also currently has engine cleaner in it but problem was there before the cleaner)
    New Fuel filter
    New plugs
    and carbies have had a can of carby cleaner emptied into them - whether that stuff does much i don't know.
    Airbox is off.

    Sorry to ask for help again, I'm sure it's stuff gumming up the carby's but just want to make sure before I start pulling stuff apart. I just wanna fix it!

    Cheers
     
    guestxc, Mar 30, 2009
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  2. sam1

    sam1 New Member

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    I believe that exup valve opens around 7 to 8k so you might want to see if that is operating properly. On my exup one of the cables was on it's last strand so that was replaced.
     
    sam1, Mar 30, 2009
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  3. dave

    dave Well-Known Member

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    The mist is not a problem as all that air gets contained by the airbox and used, as the net air flow is always through the carbs to the engine.

    Sam, the EXUP starts to open at 4000 and should be fully open at 10,000rpm, at least that's what mine used to do..
     
    dave, Mar 30, 2009
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  4. guestxc

    guestxc New Member

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    Ok well airbox on or not...there is still ZERO power past 8k rpm...and my bike is a grey 89 2KR, so no exup <!-- s:( --><img src="{SMILIES_PATH}/icon_sad.gif" alt=":(" title="Sad" /><!-- s:( -->

    So either I keep riding with it with scooter power or I'm gonna take the carby apart. Maybe enough engine cleaner and me riding all the time will work?
     
    guestxc, Mar 30, 2009
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  5. dave

    dave Well-Known Member

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    Just a though - Check the camshaft timing, as some one may have had them out to do valve shims. There is a post in the "how to" section about how to do the valve shims and put the cams back in.
     
    dave, Mar 30, 2009
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  6. dontz125

    dontz125 Active Member

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    Dave - the fuel mist is actually a bit of a bad thing, as it means that volume of air goes through the throats at least twice, getting two loads of fuel. <!-- s:-? --><img src="{SMILIES_PATH}/icon_Eyecrazy.gif" alt=":-?" title="Eye Crazy" /><!-- s:-? -->

    Guestxc - The '89 3LN1 had EXUP, as did the '88 3HX. Not to be rude but - you're sure you don't have EXUP? What you're describing is EXACTLY what happens when the valve is stuck in the low-rev position. Second thing to check, while you have the airbox off and are revving it up - when you give it a sharp bit of throttle, do the slides rise? They won't lift much under no load, but seized slides will choke off the airflow. With the engine off, lift each one with a finger, see how far it moves, and how well it returns to closed.
     
    dontz125, Mar 30, 2009
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  7. dave

    dave Well-Known Member

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    Ok Dontz, the '86 and '87 did not have exup, so there may be some confusion as to the model.
     
    dave, Mar 30, 2009
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  8. dontz125

    dontz125 Active Member

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    Not denying that, but when a fellow who says his bike is of the year that EXUP was fitted, and is having problems consistent with a malfunctioning EXUP... <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->

    Just double checking...
     
    dontz125, Mar 31, 2009
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  9. guestxc

    guestxc New Member

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    Yes there definately is no EXUP as there is no control valve/cable/box anywhere on my exhaust.

    So I've cleaned out the carbys out (taken apart) they're smooth as now - and the bike regained 2000rpm so now bike revs to 10,000 with gusto. Just dies down when i get there. I'm thinking it might be along the issue of timing as well.

    I tried my best but I think it's time for the workshop <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D --> Thanks guys for the help, I'll actually get my RWC at the same time lol, the rego ran out without my notcing haha

    Cheers all!
     
    guestxc, Mar 31, 2009
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