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

[thump*140]

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.

 

[DvDRip]

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

 

[daimojay]

Great write up mate!

Lots of good points

 

[thump*140]

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.

 

[DvDRip]

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

 

[thump*140]

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

 

[SnItChY]

hey its was worth the sticky thumpy good work mate

keep it updated to if you have anythink to add

 

[pbk]

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

 

[daimojay]

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

 

[pbk]

^^^ 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

 

[coolmodee01]

this is a good post and thump is right in saying the oko carbs are tuneable but are very hard to perfect and you will find that 1 out of 5 28mm oko carbs are lemons they have a fault in the casting and are completely un workable

they are also unusable on any stock motor you will have to port a 150 head as big as possible before it will run anywhere near good.

i'm running a mulkut 26 on my lifan and have never had an issue wouldn't mind a keihin 26 flat if someone wants to shout me one

just my experience talking here to some peaople beleive they have got big carbs running sweet on small engines but you will find they dont and if you where to put a smaller carb tuned well on there bikes they would never look back

Well done thump* plus reps for you buddy

 

[Brocko]

Mate you should do some more sticky threads on carb tuning.. It would be good to get a good thread on here from a member that we could all easily learn from..

 

[thump*140]

this is a good post and thump is right in saying the oko carbs are tuneable but are very hard to perfect and you will find that 1 out of 5 28mm oko carbs are lemons they have a fault in the casting and are completely un workable

they are also unusable on any stock motor you will have to port a 150 head as big as possible before it will run anywhere near good.

i'm running a mulkut 26 on my lifan and have never had an issue wouldn't mind a keihin 26 flat if someone wants to shout me one

just my experience talking here to some peaople beleive they have got big carbs running sweet on small engines but you will find they dont and if you where to put a smaller carb tuned well on there bikes they would never look back

Well done thump* plus reps for you buddy

Coolmodee makes a very good point with the engine capacity/carb size you run.. I chose the 28mm flatslide initially, as it was all that was available at the time, i didnt know a lot about these particular carbies at the time, and partly cause i wanted to prove it could be done.. As coolee said, and pointed out in the short guide on engine cap/carb size in the initial post, dont run a 28 on a stock motor, especially a small one.. put it this way... it wasnt that long ago, that 125 twostrokes were running VERY similar sized carbies... keeping in mind 125 twobangers run about 30-35hp, and redline around 11-12000rpm... so they draw in a lot more fuel than a 140 four stroke lifan.. at a guess, probably about 6 times the amount of fuel...
it took me a long time, and the dyno guys at Competition Conversions a long time to jet my 140 right. Timing was altered with the IRK, and all sorts of jetting combination were tried, most failed. It is running very hard now, but it was a hard road getting there. I can however, provide the specifics on jetting, for those who are running similar set-ups... ie: IRK, Big Bore pipe, Cam, head-work etc...
So yeah, i agree entirely with Coolmodee... unless you have a weapon of a motor, with the extra power parts to support the 28mm, go for the 26 or the 24mm variant..
My next plan is to swap the 28 in my 140, for the 26 in my 250 Blitz (stock engine)..
just out of curiosity mostly, to see how it alters performance. (generally, the smaller carby, the more power is concentrated at lower revs.. opposite for bigger carbies.. Hence the reason the 28mm will make a motor a top end screamer.)
Once this is done, i'll post the results up in here... will add a bit of proof to the pudding with what Coolmodee said about a smaller carby working better after tuning a bigger one right..

 

[thump*140]

^^^ 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

Not necessarily. I've run mine in both very hot, and very cold conditions, with only a marginal power drop during summer... which is to be expected... commonly known fact, that hot air=less power... That's put very basically, but it's what happens.
Jetting your bike in winter, wont necessarily mean it will run bad in summer, but you will lose a bit of power.
Altitude is a bigger problem, as the higher up you go, the thinner the air is. Consequently you have to jet leaner (I think... perhaps Mr Cactus could correct me on this?) as you are getting less O2 in, but the same amount of fuel, which would make your bike run rich... Humidity will have a similar effect, but not to the same extent..
if you live high up, jet your bike to suit, and you should be ok, unless one weekend you ride in the mountains, then the next day you take it down to sea level, and go ripping up beaches... then you'll notice the difference altitude makes.. but if you ride in the same places all the time, with little variation in altitude, you should be ok.

 

[pbk]

hey mate got my carb got it set it up its got 97 main jet got it going ang runs like an 80's 2 banger got real bad low to mid and revs out at the top.....thats when riding

when revving it its a bit crakly at low and then is a bit crapy at top, so is this jets or mixture or needle???

 

[thump*140]

hey mate got my carb got it set it up its got 97 main jet got it going ang runs like an 80's 2 banger got real bad low to mid and revs out at the top.....thats when riding

when revving it its a bit crakly at low and then is a bit crapy at top, so is this jets or mixture or needle???

Hmm... sounds like your main isn't far off the mark. something i neglected to include with the original post, is that with the OKO's, when the Main is way off the mark, the actual bottom end power and response is pretty massive... then you tune the main, and the bottom end power and response disappears, and is impossible to retrieve... without going back to the oversized main, which then means it wont rev up top.. lose/lose situation..
being crackly at low revs i'd imagine it's a combination of too lean a pilot jet, and possibly air-screw mixture settings... a good starting point for the air screw, is to screw it all the way in, then turn it back out 1.25-1.5 turns.. start the bike, and with it idling, turn the screw in or out and listen for a change in engine note. if the revs rise and drop when you turn it in or out, then you have the right size pilot jet... if it makes no difference, your pilot jet is either too small or too big..
Mine is still a bit "fluffy" down low in the revs, but we found it impossible to tune that out, with either jetting or ignition timing... but this is due to the fact it's a massive friggin carby, and the engine doesnt quitttte breathe enough for it..
I'm going to pull mine apart tonight, and see just what jets it's running exactly, and post them in here in the morning. It's been over a year since we jetted it, so i cant remember off hand what the jets were aside from the main jet...

What size carby, and what size engine are you running? Those details might help in troubleshooting your probs..

 

[thump*140]

update/hint for the OKOs..:
if you must insist on the 28, like i did..... :$ then to gain the most out of it, use an IRK and a hydraulic clutch. Neither are expensive, and both will assist in letting the motor grabs revs a lot quicker...
pitbikekid made a good point... these carbs do feel a bit like an 80's air cooled twostroke... (think engines before powervalves were invented...) almost, almost, allllmost, alllllmooooooosssssssstttttt BANG!!!! On the Pipe and Holllleeeeeee Shhhheeeeeiiiiitttt theres the power...!!!!!
they do feel a bit doughy and slow to rev until they come into the top end... or conversely, onto the main jet... If you can use a bit of clutch to get the thing to rev, the power is instantaneous and will really get you moving if you can stay on top of it... and of course, the IRK will let your motor grab revs quicker... thus making it easy to flick the clutch, get the revs up, and get the carby into it's warm happy place... And the hydraulic clutch, seems to actuate a little quicker, is lighter, and looks horn...
Have had one fitted to mine since it was conceived/born/built whatever you want to call it, and have never had a problem with it.. never had to adjust it, never had it fade, even in hot weather with heavy use... pretty impressive for $30 from Egay...

 

[pbk]

mine has a k36 slow and im running a stock lifan 150 also the carb is 26mm flatslide oko

 

[pitsterproAUS]

make sure the needle in the flatslide is JJH

 

[daimojay]

i can tell you now that the MOKLT 26mm is killing even my 155cc motor... but having said that, my head and everything is far from stock.....

Im using a TM33 on my 187 and 194z motor but they have the accel pump which makes up for the bottom end. The pumper carbs are something to be suprised about.... even though its a 33mm you need to realise that some of these motors are putting out impressive figures!

I know i ran the MOLKT 26mm on my lifan 120cc with a IRK, ported head and a cam... it was mint!

really it all comes down to the abililty to jet it right and roll on the throttle instead of just opening it WOT.