the carby situation,guidelines needed...

[Mack]

They are very sensitive to the main jet setting and needle position from what I've seen so far, but really let you know when you have got it right. I have only tuned one of these 26 oko carbs but on a modified engine so your settings may differ, but, the 102 main will work although it is on the rich end of the scale. Will need to carry a 100 for when its needed. Guys in the states seem to be settled around 100 main on built 146 GPX's.

I have read US guys recommending a 50 idle jet, but this seems big.

 

[MasterSpoon]

much appreciated mack
I will have to look around and see what jets i can get easily and see if maybe a small collection is cheap enough.

 

[Mack]

I have just got my hands on another of these 26mm carbys and am going to use it on an engine i am building. Stripped it right down today to have a look at the drillings and might have a crack at porting and redrilling this one to see how well can get it to work. The beauty of the 26 is that it most closely matches the spigot, manifold and port diameter to give a straight induction system. I will leave the bottom third of the throat at 26mm for good low end vaccum but open the top out to 28-29mm. I'll order a heap of idle jets and let you know what works.

 

[Cactus Jack]

It'll be great to see what you come up with mate ......

Numroe's 26 OKO worked pretty good because he has a decent pipe ....... but he quickly realised how important the intake flow is too ... validating what I said about "the filter with the biggest surface area will be the best " and "carry spare filters for regular changes throughout the day to maintain optimum performance" ....

Most of the others will be having issues because they haven't got the flow balance at optimum levels right throughout the entire system ....

 

[MasterSpoon]

Quick question guys, any good cheap online stores (prefer in Aus) that have the Keihin jets? thinking I will have to get a few different sizes in the pilot and getting real sick and tired of the stupidity of the local stores.

Took the two jets around to some stores today and told the people at the service counter I wanted these Keihin jets but in X size, normally the first question was "what are they out of" I just looked at them like they were stupidly and said "a Keihin carbie......". None of the shops had the sizes I wanted either, pilot was in stock at one place and had to order main from another.

 

[Mack]

I have no idea what to tell you now as I worked this carby over a bit and the engine is probly a lot different than what you have. I started out putting a big idle jet in and left the 102 main to run in, but soon realised I was way too big for this engine setup and ended up back at the 37 idle jet before long. But I am running the next finest needle taper.

As usual allowing the head to breath changes everything. This carby, modified, is dynamite on this 150cc engine I just finished. Very happy with the results...

 

[MasterSpoon]

good to hear Mack
I am still running mine as it came basically just adjusted the 2 screws and it runs nicely, when I get my exhaust done I will rejet and properly tune tho.

What have you done to modify yours?

 

[edzy]

i rang ken b4 and im getting a oko flat slide 26mm for 70 delivered
i told him i didnt want the manifold or filter or throttle cable

just getting the carb and the manifold adapter.

its for my stocky dhz . will the jets be fine for it or is changing them a must?

thanks

 

[Mack]

good to hear Mack
I am still running mine as it came basically just adjusted the 2 screws and it runs nicely, when I get my exhaust done I will rejet and properly tune tho.

What have you done to modify yours?

Port, polish and shape. Helps to think of a carb as a miniature head. Clean up all entry and exit points of passages, remove burrs from fine drillings which may be disturbing flow and/or redrill if needed. Surface all sealing joints to be sure of perfect seal and then some reshaping of the main carby throat, leaving 100grit finish on the fuel/air side of the slide then polish air only side back to main opening. Also the rubber adapter is attached and honed out perfectly to match both carb and manifold. From carb opening to valve there is not a bump or lip in sight. The reshaping is done from 1/3 slide opening and up. Also the larger radius across the toip of the throat is gradually introduced or tapered you could say from front to back. This means at low throttle openings this carb thinks its a 26mm, half throttle a 27-28 and at WOT it morphs into a 29mm.

 

[numroe]

$#@! Mack. That's border line obsessive compulsive disorder with engine tweaking. I like it!!

I love my OKO26 on the Lifan 140. No way perfect (never read this thread until now) and it sounds like I got a little lucky. My setup:

Always near sea level. Air temps between 23 and 33 not making a huge diff but humidity does (eg. humidity 50% versus 85% and I change the main jet).
I never drilled anything.
Screw = 1.75 (approx).
Slow = #38 (stock was #37. Tried 36 and 40. Have no 39).
Needle = 1 richer than mid.
Main = 100 or 102 (depending on the day). So quick and easy to change it. Have K95 to K105 in 2.5 steps.
Float level raised twice since new. Measurement = ??
32mm exhaust. 41mm muffler. But too loud
Inox oil on the slide and inside the cable.
Manifold rubber join: I chamfered (knife cut) and smoothed away (sanded) the step lip so the 26mm carb exit joins progressively to the 25mm alloy inlet.
Inlet: Hand sanded inside it with about 80 to 180 grit. It was UGLY in there.
CDI: stock. Coil: Akunar (orange). Plug: CR7HSA (by memory).
Filter: I have two options:
A) 48mm entry Unifilter 70x100 foam. Mounted directly to carb.
B) 62mm air duct snorkle. smooth bend to filter mounted under seat. Filter = 60mm entry. 80x100mm foam unfilter.
With either option: I can fit my extra stage filters over the core foam elements and the engine stills runs fine. Engine runs the same with option A or B. But B gives me much more options.

I was seeking nothing besides the ability to snap open the throttle at will. So I believe I am just slightly rich for the whole range. And a full rev out at any given throttle posn is compromised a little. And the jetting seems sensitive to one day versus another. But the only time I wait for a rev out is in 4th, and with 15:39 gearing I have no mini track needing that top speed.

I began by setting the screw to get a decent idle. Then by snapping the throttle to 1/4 open to set the slow jet. Then snapping to full open to set the main. Then from idle to 1/2 to tune the needle clip. Then I went back to checking the slow jet.

No throat "morphing" for me Mack. My engine aint no revver really. But she has grunt on demand. I love it, because it gives me huge room for error around corners. To be honest for a carb with no accel pump I am stoked. So many guys with FCR39 to 41mm AP carbs have bog issues.

Why am I so lucky? I suspect my Fuelstar TM-VC gizmo has a bit to do with the ability to burn a slightly rich mixture with little bad effects. A good experiment will be to go back to the Mikuni 24mm and work on it as best as possible and compare to the OKO26.

 

[tubes380]

mack would you put up some photos of the worked carby if you dont mind

 

[Mack]

sorry not to get back to this one guys, I check back after an email notice, of which I had none...

$#@! Mack. That's border line obsessive compulsive disorder with engine tweaking. I like it!!

Yeah well the way I look at china stuff is that you buy it for nicks and turn into better than name brand yourself. Thats where the saving is.

I will take some happy snaps when I get a chance. It is only about an hour long job to do the described work. These carbs are a sinch to strip down. About 2mins. To shape them I clamp a drill in the vice and wrap a 1" drill bit in the grit I want. Set the drill to slowish speed and lock the go button. Cheap carby hone. Bolt the rubber adapter up as well and do both together. Dremel for the rest. The biggest thing you notice after this work is that the carb is no longer as sensitive to low speed jetting. The smallest jet (the 37 stock jet) is actually a little on the rich side now but is running without issue, for the sake of cooling the piston and valves and to avoid detonation I am happy to leave it that way. There is no bog whatsoever, anywhere. Only power. Although this is a lot to do with the entire setup.

 

[Cactus Jack]

I can confirm the filter is quite good with dhz oko kits shame the carbie was not as good, for all you guys wanting to get the oko carb a word of warning these carbs have not been drilled correctly and require moding to get rid of the bogging (flat spot) the pilot hole requires re drilling as does the air bleed.

For all the guys wanting to tune these things My 28mm was a shocker bogged off idle and missed like crap over 1/2 throttle and mine was on a 250 ohc big bore motor so air flow was not the issue, I have re drilled the pilot bypass hole with a 028" (may go tad bigger here .030" or .032")drill and main air by pass hole to .038" but works a treat atm and I run a 39 pilot jet and 130 main jet hauls ass now no bogging. Small carb I would drill the same with smaller main fitted 110 or 115 should work 120 for 28mm i feel would be a better choice hope that helps some of you guys tearing out your hair over oko flat slides or even better get a mikuni tm

Hey Mack , did you have to redrill the holes out bigger as stated by Phrozin ???

 

[epod]

28mm OkO's are great, but dud's exist.

I have tuned 3 28mm Oko's to various lifan motors with 28mm pipes and 32mm pipe's some ported heads others not. Can always get them working fine with a uni filter and some tinkering. Only had to run a smaller pilot jet for a worked 134cc.
I am told by other mechanics that carbies can be faulty from the factory alot, does not matter what brand they are. Believe it or not.
Ride on.

 

[Cactus Jack]

Here's the carb you'd get if you wanted the best overall performance ... It's set up for 4 strokes ... Notice no wanking huge sized jets yet it has a genuine 28 mm venturi and is a GENUINE Mikuni carb with Mikuni jets ??? ... A certain sized hole can only flow a certain amount of air at atmosheric pressure (it's the highest at sea level) ... and that amount of air can only handle a certain ratio of fuel added to it to stay within the known ratios that combustion engines work best at ... so you just KNOW when you see clowns claiming to be making big power with idiot sized jets like 145 to 210 (Mikuni sizes) that they're having themselves on ...

Allens Performance Mikuni & Keihin Carbs

You can also sleeve bigger carbs back to a smaller size to increase the air velocity ...