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Zeal misfiring @7k - what next?

Discussion in 'Yamaha 250cc In-Line 4's' started by TrashedZeal, May 15, 2016.

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  1. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Dump the 98 and put some new 91 in it

    The FZX has a detuned FZR engine with BDST26 carbs with twin 2 into 1 headers

    Does it have a fuel filter on it ? ... is it free flowing and new? ... is it on the right flow direction?

    Are the spark leads on the correct cylinders? ... 1 coil to #1 and #4 and the other to #2 and #3?

    Coil test .... for the FZR but Im guessing the same for the Zeal

    Primary : multimeter on 200m (ohm side)
    probes on + and - terminals of coil

    primary should read around 2.8 ohms

    Secondary : multimeter on 20K (ohm side)
    The secondary windings are isolated from the primaries. These are double-ended coils, so measure the resistance through both spark wires (without the caps).

    secondary should be around 15K ohms




    Worn needles will affect your low end

    Check the jets are correct especially the mains

    zeal carb specs.jpg


    Heres wat a stuck slide looks like .... in this case the diaphragm was pinched on #1 when rebuilding the carbys


     
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    GreyImport, May 15, 2016
    #21
  2. TrashedZeal

    TrashedZeal Member

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    I just want to shout out a huge THANK YOU to all who replied. I can say I've found the problem, and it's largely fixed!

    Watching GreyImport's video showed me that my vac slides were far too dull in their movement - so I opened up the carbs again. They weren't stuck, but they were no where near as responsive as the ones in that video. On a hunch, I added a little (lot of) rubber grease around the tiny little top cap o-rings (3FV-14147-00?). Previously I must have put them in with a little WD40, but obviously that wasn't enough.

    Well holy crap, the difference from something so tiny is huge! Obviously the pistons are fresh so I didn't flog it too much, but it pulls really clean from 5-12k, and pulls really well for a 250!

    I now have a slightly different problem, in that 2 of the vac slides are jamming open after a WOT run, and so it runs like a pig on the needles now after it's had some throttle. They all have the factory spring(s), and the large washer in the cap still in place. I'm wondering if there's anything I can do to lube up the slides, or maybe polish them?
    I've removed them previously and they have no imperfections, and are quite smooth with no real wear marks or nicks. Looking at Yamaha, new diaphragms/slides are $143 a piece, so I'd rather fix what I have if possible. A slightly stiffer spring or a larger washer to add some preload would affect the on-throttle tune too much I would think?

    Once again thank you to all, you were all mostly correct and I was chasing my tail haha.

    Cheers,
    Jared.
     
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    TrashedZeal, May 17, 2016
    #22
  3. kiffsta

    kiffsta Senior Member

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    you bloody beauty!!!
     
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    kiffsta, May 17, 2016
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  4. Damus

    Damus She is a BEAST and riding it is comparable to sex Dirty Wheel Club

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    Heyyyy I did say "a throttle slide being jammed and not opening". If that is the problem more than likely there is a air circuit in and out that allows them to open freely. This can either be part of the slide or somewhere else, if it is part of the silde ull find a small hole in the center of the slide that goes to the carbs intake, if you clean it out properly you should get better response.
     
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    Damus, May 17, 2016
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  5. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    The Zeal carbs use an improved needle design (it is backed a spring and a plastic retainer) to keep them from wearing out, as happens on the 3LN1-3LN5 carbs. 3LN6/7 changed to the same design as the Zeal.

    I would coat the diaphragms in inox mx3 and see if they still stick. Lubricate the springs and all other parts while you're in there as well.

    You could also use an air compressor to blow air through all the jets and air circuits
     
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    Last edited: May 17, 2016
    Linkin, May 17, 2016
    #25
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The top cap o-rings are not that tiny. They are fat little things.
    [​IMG]
     
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    maelstrom, May 17, 2016
    #26
  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    The originals end up rather flat instead of fat after 25 years :D
     
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    Linkin, May 17, 2016
    #27
  8. TrashedZeal

    TrashedZeal Member

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    Thanks I'll give that a shot, hopefully that cleans up the bottom end. I don't actually recall seeing that hole so chances are it's blocked!

    I've used a compressor on all the other jets and whatnot with some carb cleaner as well. I'll try the inox on the diaphragms and springs and see if that helps along with Damus' suggestion.

    Yeah that's the ones. Relative to the problems they've caused me, they're tiny haha. Thank you for your product by the way, everything was awesome. I note you mention that some rubber grease is required in your assembly instructions... it might pay for me to read those next time haha.
     
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    TrashedZeal, May 17, 2016
    #28
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