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  1. #1

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    For Those about to Rock... buying OKO Flatslides..

    Ok it seems a lot of people on here are considering buying OKO flatslide carbies in the hunt for a bit more performance.
    Then it seems like everyone who considers it, finds out that the Flatslide is hard to tune, and doesnt buy one.
    They arent hard to tune at all. No harder than a mikuni or molkt or anything like that. They offer great performance when they are tuned, BUT THEY ARENT FOR EVERYONE.
    They are better suited to a more experienced rider, as they are a bit touchy with delivering the power, especially when used with a 1/4 turn throttle.
    Basically a flatslide equipped mini, is like riding riding a two-stroke 125, without the outright power... bottom end grunt isnt great, but it builds into a good mid-range, then a screaming top end.
    They will transform a stock motor into a bit of a top-end tearer, but they are best used on an engine that has had a bit of work done to it, such as an IRK, Big-Bore pipe, cam, or head work that makes the most of the breathing capabilities of the flatslide.
    I run a 28mm flatslide on my custom 140 lifan, and a 26mm flatslide on my Atomik Blitz 250. Both bikes experience substantial gains when the flatslides were added, and both went from having reasonable power overall with the standard mikunis they came with (24mm and 26mm pumper respectively), to having power that built strongly in the mid range, into a screaming top end. Seems to be a bit of a trend/quirk with the Flatslide.

    Most of the threads on here state the OKO flatslide as being hard to tune. They are no harder to tune than the mikunis, but generally are delivered with jetting that is way off the mark, particularly the main jets. My 28mm came stock with a #195 mainjet... which is about twice the size needed.
    It seems OKO grab whatever main they can see, and chuck it in...
    The OKO Flatslides are great carbs to WORK on.. The main jet can be changed without removing the carby from the bike, through the drain plug, the air-screw can be adjusted from the left side of the carby without removal from the bike, and the needle jet can be accessed by loosening the rubber manifold clamp that comes with the carb, and tilting the carb on its side. Try tuning any jets on the mikuni without removing it from the bike... depending on the bike you have, you MIGHT be able to do the needle... So as far as working on the carby itself, the OKO Flatslide just reeks of pure WIN...
    Like the mikunis, the OKO's have a pretty standard starting point when it comes to getting the jetting right... the pilot, air screw and needle are pretty much on the mark.
    The mains are the problem. I've found that they are jetted very rich standard, but the thing that seems to make them so hard to tune, is that they give the opposite symptoms from the problem. IE: they seem like they are running lean, when they are actually running very rich...so you throw a bigger main jet in, and get further and further away from getting it right. Took me a LOOOOONG time, and lots of dollars in main jets to figure that one out... sadly plug chops dont always help with the tuning, as they just dont run/burn until the jetting is right.

    So if you get one, leave the pilot and needle as they are...
    When you buy your carby, request that it be fitted with a #95 main jet. Like the mikunis favour the #92 mainjet (which coincidentally is quite a bit different to the OKO #95 main jet, and not just 3 numbers out..), the OKO's are best started off with a #95. This will allow it to at least run well enough to do an accurate plug chop, and alter jets from there.
    My 140 running the 28mm, was dyno-tuned, and gave out AFR's (air-fuel ratios) of around 12... which is pretty close to "perfect" tuning and safe either side of too much or not enough fuel... and that's with a #95 main..
    Making sense yet? USE A #95 MAIN TO GET YOU STARTED.
    Coincidentally, if you need to buy main jets, go to a dyno shop, they'll have heaps on hand, or alternatively, if you want to buy new ones, go to a Honda shop, and tell them the jets are the same as the Keihin jets used in the Honda CR-F 250...

    Oh and finally, select the right carby size, for the motor you have. Dont throw a 28mm flatslide on a 110 motor.
    use this as guide...
    110-125 motor, no mods : use a 22mm or 24mm flatslide.
    125-140 motor, no mods: use a 24mm
    140cc with mild mods/150 or 160 no mods: use a 24mm or 26mm flatslide.
    140cc with wild mods/ 150 or 160 with mild mods: use a 26mm or 28mm.
    140-160 rocket ship motors: use a 28mm
    150-250 Loncin/Zongshen upright motors- no mods: use a 26mm
    150-250 Loncin/Zongshen upright motors with mild to wild mods: use a 28mm

    So in closing, the OKO flatslides arent hard to tune. They're bloody easy to tune, you just need the right starting point. They are, admittedly, a little harder to get PERFECT compared to the mikunis, but i've found the OKO Flatslide when jetted close to perfect, offers more performance than the same size Mikuni jetted perfectly. obviously people will disagree, just sharing my experiences having run both types of carbies on my bikes, especially the modded 140 and 250...
    keep in mind they will make the power a little more "light-switchy", but if you have the skills to ride one, ie, if you're a good 125 two stroke pilot, then the OKO is the fuel bucket for you!!!

    If anyone has questions in regards to tuning them, fitting them, or want to add more info, please go nuts on here...
    The OKO is a great carby bang-for-buck, and much more user friendly maintenance wise than the mikuni.
    Last edited by thump*140; 28-07-2009 at 01:04 PM. Reason: clumsy typo

  2. #2

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    Yea I'm a n00b rider so I don't like the idea of on/off power with the flatslide, and I use the bike for trails mostly so I'm more into bottom end grunt, thanks for this info I'm sure it'll help allot of people decide if they want a flatty or not
    Last edited by DvDRip; 28-07-2009 at 12:48 PM.
    ┌∩┐ ◣_◢ ┌∩┐

  3. #3

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    Great write up mate!

    Lots of good points
    YX187

    Takegawa S-cut (67mm)
    stock crank (53mm)
    TM33
    TBv2 with extensive porting
    s35 cam
    32-37mm exhaust
    DNM M200
    DNM MT-Bag
    Pro-taper high rise.

  4. #4

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    Quote Originally Posted by DvDRip View Post
    umm well this is about the roundslide....... do you think a 95main would be a good starting point for this too? and does the roundslide take the same jets as the flat?

    Yea I'm a n00b rider so I don't like the idea of on/off power with the flatslide, and I use the bike for trails mostly so I'm more into bottom end grunt, thanks for this info I'm sure it'll help allot of people decide if they want a flatty or not
    yeah i would imagine a 95 main would still be a good starting point for your bike/carby. best way to get your initial starting point, is before you put the carby on, take the float bowl off, and check the main jet for it's size. The keihin jets will usually have it stamped on the side of the jet, so you may have to quickly whip it out to check. it coule be anything from a #87 to a #195 going from experience, ha ha, so if it's somewhere in the nineties, you should be ok. attach the carby to the bike, and ride it at different throttle settings.. if it revs cleanly off the bottom, doesnt die when you crack the throttle, you should be ok for the needle and pilot jets. If it runs ok at WOT, you should be alright with the main. If it coughs and farts, or just dies altogether, and you are already know that you are running say a #95 main, then it makes it easier to know where to go from there... A stock Lifan 140 wont need anything bigger than a #95 main, so go down in steps of 3 until it runs cleanly from idle to wide open throttle. ie: go from a 95 down to a 92...
    but yeah, i reckon you've made the right choice with the roundslide. I'd imagine the outright power would be the same close to the Flatslide, but the delivery would be far less savage.. and when trail-riding the flatslide, they have a tendency to surge a bit.. but that can be cured by using a normal throttle, and not a 1/4 turn...
    good luck!! any more dramas with the jetting, post back in here, i'll keep an eye on this thread...
    Have spent a loooooot of time playing with these flatslides from OKO, starting to pick up a few tricks with em.. if i can help a couple of people out, it's worth it.

  5. #5

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    nice one thanks allot mate
    It's a brand new engine too so I hear I should only tune it roughly to an acceptable level then fine tune once I've run a couple tanks through
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  6. #6

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    yeah that's a good point... when doing your plug chops on WOT take it to wide open until you hit close to the limiter, then back off straight away... you dont need to hold it wide open for ages to discover if it's rich or lean.. if it's wrong, it will tell you straight away, by either coughing and farting, or just dying altogether... if you get it close, that will do until it's run in, then you can start thinking about doing your valve clearances, and jetting a bit leaner to get optimum performance. when you do this, keep in mind that for trailriding, a little on the rich side is a good thing, as you tend to spend more time with the throttle open, as opposed to mx where you are going from WOT to closed throttle on and off..

    oh and cheers to whoever made this a sticky... makes the typing when i should have been working, worthwhile. ha ha ha

  7. #7

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    hey its was worth the sticky thumpy good work mate

    keep it updated to if you have anythink to add

  8. #8

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    though i have read somewhere that where you live does affect your jetting as different air temperatures please confirm if his true or just BS
    NSW Miniriders Crew


  9. #9

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    no thats true, air temp, altitude, humidity all effect the jetting
    YX187

    Takegawa S-cut (67mm)
    stock crank (53mm)
    TM33
    TBv2 with extensive porting
    s35 cam
    32-37mm exhaust
    DNM M200
    DNM MT-Bag
    Pro-taper high rise.

  10. #10

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    ^^^ well thats sort of where i was getting at seeing as where people live could be differnt alltitudes and so on

    so does this mean if i set my flatslide up in winter that its gonna run like crap in summer??? seeing as where i live i usually get some pretty humid summers
    NSW Miniriders Crew


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