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Discussion ZXR 250 Carb Slide Mod

Discussion in 'Kawasaki 250cc In-line 4's' started by venom80, Mar 4, 2014.

  1. venom80

    venom80 Loud pipes save live's

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    Iv heard of a guy in New Zealand drilling a 1.5mm hole into the slide diaphragm of the carbs, the idea behind it is to allow the slides to move quicker thus faster acceleration. Not really a performance mod more so just quicker throttle response. This same guy said the ZXR 400 guys who are racing do it all the time but bigger up 3-4 mm per carb.
    Thoughts Please
    this might be some thing I would like to try if the results are there to be made?
     
  2. cal

    cal Well-Known Member Premium Member

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    i have watched that video, not too sure about it? especially because his bike has got problems that he cant solve.

    dont drill the slides untill you can get some more reliable evidence - to my knowledge nobody here has attempted this, *looks to Kiffsta*
     
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  3. Jim

    Jim Active Member

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    Apparently it's a pretty common mod on bikes with CV carbs. I haven't done it myself but have always been tempted to. You can always seal the hole with some RTV if it doesn't work out.
     
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  4. venom80

    venom80 Loud pipes save live's

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    I did bit more looking around the net last night and yeah it is a common mod for CV carbs. dynojet do kits for bikes complete with new jets and drill bit to suit. The next question is how big to make the first hole, my bike is running a bit rich so i was thinking that 1.5mm - 2mm should be ok it should not lean it out to much, maybe :confused:.
     
  5. zixxer

    zixxer Well-Known Member

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    i was thinking this too, still the video is good to learn how to get the carbs off.
     
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  6. cal

    cal Well-Known Member Premium Member

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    yeah he helped me out with that vid when i first did the carbs :)
     
  7. Jim

    Jim Active Member

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    I think you can get away with just taking the fuel tank off to get to the caps off.

    I don't think doing this mod will affect the air/fuel ratio, but correct me if I'm wrong.
     
  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Some more on this subject.
    The Yamaha FZR400 3TJ1 race kit manual, available on my web page for that model's carb kit, shows as follows.
    SlideMod.jpg
    Now if only there was a race kit manual for the ZXR250.
     
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  9. ajverma

    ajverma Active Member Premium Member

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    I've done this mod to my A model :)

    I drilled 1.5mm holes in every slide next to the larger hole.

    Works fine, can't say it makes a gigantic difference unless you're well tuned to your bike. IMO a quick action throttle tube from a later zx6r or something is a much easier way to achieve the same seat of the pants result.

    I've got my a/fs 2.5 turns out, and with this mod it does rev quicker, but it's running too rich right now so I wouldn't be able to give you a 100% idea.

    I can take some photos when I have the carbs off later this month, so you can see what I've done.
     
  10. venom80

    venom80 Loud pipes save live's

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    I spoke to mate this about this and he told me that he's done this mod to his dr600 and high recommended it, but he suggested drilling a hole the same size as what is already there which would be around 3mm maybe.
     
  11. kiffsta

    kiffsta Senior Member

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    I have a full of diaphrams if someone wants to try it
     
  12. venom80

    venom80 Loud pipes save live's

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    How much do you want for them?


    Sent from my GT-I9300T using Tapatalk[/quote]
     
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  13. zixxer

    zixxer Well-Known Member

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    had a look at some quick action throttles but not sure which will fit properly.
     
  14. zixxer

    zixxer Well-Known Member

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    just looked up part number for the tthrottle and its 46019, saw they fit the zx7 aswell, cant find any for sale in aus though.
     
  15. kiffsta

    kiffsta Senior Member

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    [/quote]
    $10 each
     
  16. ajverma

    ajverma Active Member Premium Member

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    Hey zixxer, I've put an 06 model zx10R one in my zxr 750, I know this will also fit the 250 as it
    has the same diameter tube as pretty much any kawasaki sport bike litre and under, best bet is just to ride to a wrecker and take one off a broken bike for $20 or so
     
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  17. Jim

    Jim Active Member

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    That reminds me. The aftermarket jet kit that came with my bike also came with instructions to clip the slide springs. Start with two coils and work from there. I think the combination of the two mods will give a greater result.
     
  18. venom80

    venom80 Loud pipes save live's

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    So today I decided to bite the bullet and go ahead with adding a second hole to the slides. As you can see from the photo I used a 2.5mm drill bit. The whole process was very quick and easy start to finish in about 1.5hrs.
    I can feel a good difference though out the rev range the bike is quicker going though the gears it also feels smoother and a more positive feel on the throttle. I think its helping it start easier But I'll keep an eye on that one over the next couple of days. I'm going to see how it goes over the next week or so and then I might drill a third hole and see if I can get it going quicker some more or am I getting greedy :neo:
     

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  19. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Too much and you will have the slides jumping up so quick it will 'stutter' when you crack the throttle.
     
  20. venom80

    venom80 Loud pipes save live's

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    don't you think that the spring would help compensate for that though
     

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