Keihin PWK copy carb mods

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sean01

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ok since there seems to be more and more of these carbs showing up i thought id do a little guide on some mods that can be done to improve these carbs in both tune-ability and performance

this guide is mainly aimed at the people that have purchased one of these carbs in the hope that they are an exact copy of the OKO/genuine PWK.

try to avoid buying these cheaper carbs as it takes a bit of time to mod and tune them to get them to run nice compared to the OKO carb.

the main feature to look for is the fuel bowl, if they dont have he large hex drain screw in the bottom then they run the small round jets...


ok to start off with ill list the differences between the cheaper copy carb and the OKO

1.the copy carb runs a different emulsion tube(main jet holder)
and has a different amount of holes in it. OKO has 8 holes the copy PWK only has 6.
also the copy carb runs different main jets (small round keihin jets)
OKO emulsion tube is a direct replacement
100_5301-1.jpg


2. they run different fuel bowls, the copy carb doesnt have the large fuel drain nut on the bottom. (not pictured but very obvious)
OKO fuel bowl is a direct replacement

3.most important difference is the copy carb runs a smaller float valve.
pictured is 2 valves left is OKO right is the pwk copy valve.. massive difference
and also the copy carb lacks 2 holes drilled into the side of the float valve boss.
Untitled.jpg


4.in some of the cheaper pwk copy carbs they have a NON chromed D slide(flat slide). (again not pictured but very obvious)
OKO chrome D slide is a direct replacement

5. the throttle top on the carb is also different and lacks the angle throttle cable stem, not a big issue but be sure to make or find a rubber boot to fit over the top to help keep dirt and water out.
OKO throttle top is a direct replacement

6.in most cases these pwk copy carbs are assembled with jets and needles with no markings on them so its a good idea to replace these with genuine keihin items.


ok ill show you what mods i have performed and worked well..

firstly the float needle hole needs to be drilled out in 2 locations.
the center flow hole needs drilling to 2.5mm

now the OKO float valve is 5.2mm so drilling with a 5mm drill bit will allow for it to move freely in there.(when ever you drill something the hole always ends up larger than the bit by a fraction.

be sure to keep the drill square with the float hole and fasten the carb in a vise(just firm pressure is enough)

also while you at it drill the side of the float valve boss with a 2mm drill bit, line it up about 3-4mm above the flat valve seat and go right thru both sides.(closer is better but no more than 2mm)

also the float level height should be 21-22mm measuring from the highest part of the float to the fuel bowl gasket surface..this measurement was taken before any mods performed and also confirmed against the OKO carb but be sure to measure yours before any mods
i used a china keihin copy carb float valve(PZ26) in my mod, they are exactly the same as the OKO float valve
100_5296.jpg


finished product

100_5304.jpg

100_5305.jpg


these 2 mods i havent done on my own carby's yet but i have witnessed the improvement on someone elses. when i get a jet drill kit i will perform these without a doubt.

ok these mods only needs to be done if your having trouble with a bog spot in the lower rev range (1/4 throttle area)
its hard to show you where to drill but if you totally remove you mixture screw and look from the air filter side of the carby youll notice a rather large hole, in tht hole is a tiny hole it runs into the emulsion tube area.
the OKO hole is larger than the pwk copy hole but not by much.
so make sure the emulsion tube is out and use a 1mm drill bit and drill the tiny hole out.

you will need a drill with a small chuck to hold the 1mm drill bit, or better yet use a jet drill kit. also i cant stress enough to be very careful here, if you snap the drill bit it will be extremely hard to get it out.

if your still having problems with a bog spot but they arnt as bad then do the following mod first before slowly go larger with the hole but dont exceed 1.6mm
100_5303-1.jpg



ok this mod requires you to drill an extra hole in the emulsion tube at the thread end of the tube..
PLEASE NOTE..if you install an OKO28mm emulsion tube then this mod is not needed unless there is still a slight bog spot
IMG00038-20100224-2051.jpg


the next mod is a simple mod but requires you to purchase a proper OKO choke mech. all of the pwk copy choke mechs i have come across are utter rubbish.

the choke simply unscrews and you screw the new one in.

Extra info

ok probably the best thing you could do is buy an OKO 28mm rebuild kit

also thought id mention too that the total length of both emulsion tubes with jets fitted is the same (as seen in picture 1), so i cant see why you would need to change the bowl to run an OKO emulsion.

also for some reason every 28mm pwk no matter of the brand has required larger than normal pilot jets to get it to respond on the mixture screw.
my pwk copy runs a 52 pilot and 95 main on a standard yx150(klx)im about to go 98main tho
the OKO carb runs a 42 pilot and 110 main on a 176cc yx150(klx)
both run JJH needles at different heights

Ken @ DHZ should carry all the OKO parts you would need, i purchsed just a chrome D slide from him when i replaced mine.
but there are plenty of online places to get these...

few links of interest (will update as time goes on)
DHZ Mini Moto
OKO Australia - Flatslide Carburettors Thanks Tina
treatshq treatland.tv moped puch superstore discount parts for the people! replacement OKO bits, good prices
AKUNAR CARBURRETORS make sure you order by email
http://stores.ebay.com/Scooter-Assassins-in-US/_i.html?_nkw=oko&submit=Search&_sid=311188738
eBay Australia Store – ozmestore1: Search results for jet drill. jet drill kit (hmm my favourite ebay store)

if anyone has info they want to add post away..
 
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sean01

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china dont confuse this info with your carby, yours isnt a cheap knock off.
you have the correct bowl and main jets..

also where you see 3 bolts on an oko. the oko i have and all the ones i have fitted over the years have had 2 fuel bowl screws

and thx Tina for the link, tht one totally slipped my mind...
 

themountain

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nice info .. :D..don´t forget to mention ,that for some engines(160cc and above) you have to get a stronger slide spring ,because the engine signal is so strong, that the genuine spring keep the slide open in some situations ;)
 

sean01

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cheers roost.

the slide spring problem isnt really heard of over here, and have never experienced it myself..
but i do like to put a stiffer spring in as i think there a little on the light side, specially for track work.
 

Mack

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The weaker spring shows itself when you get the tuning just right and using big cams. Will hold the slide open for a second at WOT when you try shutdown. A bit disconcerting at the end of straights...
 

caesar

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Hi newby here.
I am looking for a keihin PB 24mm carby for my postie bike
cheers Caesar
 

RED519

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Mate, can you give me idea how JJH needle looks like? or can you post pic of JJH needle and the stock needle of PWK?
Cheers,
Red
 

sean01

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needle size will change from different models..

pointless showing a picture of it too, as the changes are rarely visual to the eye..

needles have the size stamped on them just under the clip grooves...

check out akunar.com , he sells them and is in thailand
 

RED519

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I mean PWK 28mm. You said I need to change with JJH needle.
Have you tried buying carby at akunar.com? I wonder why their PWK is a way cheaper than other site. Are these PWK at akunar is a china copy of genuine kiehin PWK?
 

sean01

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thought id throw a bit of an update in...

i emailed OKO Taiwan just recently and asked them about a few certain issues..

the main issue being that OKO carbs bought from china are in fact 100% fake carbs and if anyone has purchased any Chinese OKO's they will notice the lack of hex main jet and different emulsion tube.
for those who have purchased a hex main jet style OKO carb from china, you got lucky..

so basically word of warning... dont buy an OKO carb from china unless you have photo evidence that it runs a hex main jet...
 

IAMTG

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Thought I would update an old thread to keep it current. The copies are getting better, but are not quite right yet.

I have attached the photos to show some fixes they have done over the years but they are still not right.
oko30copy7.jpg
oko30copy6.jpg
oko30copy5.jpg
oko30copy4.jpg
oko30copy3.jpg
oko30copy2.jpg
oko30copy1.jpg

Obvious differences are the Emulsion tube, the air screw, the unmarked jets (with round main not hex) the casting was left with a bit of flashing that I have already removed and there are only 2 holes tapped for the float bowl not 3. The metal float bowl only uses 2 screws but original OKO's I have heard have the 3 holes in case the plastic bowl is used.

Notice that since this forum started, the float valve and the hole in the float valve boss has changed to match OKO.
 

my67xr

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have you measured your slide to see if they are now using the smaller genuine OKO one, or still the chinese one ?

and are you running the power jet, if so what Main Jet ?
 

IAMTG

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The Slide will be a fake Chinese. The amount of crap left in it that had to be cleaned out screamed of poor Quality control. Remember that a real Keihin has a polished stainless steel slide. The OKO and fakes have a chromed steel. The chromed steel are actually slightly bigger and will not fit in a Keihin and a Keihin slide will be too loose in a copy.

From what DHZ told me its not a power jet but a specific port used only for the Gy6 150cc scooter. The only OKO with a genuine power jet is a 24mm.

The jetting that came with it is all un marked. Came with 2 spare sets of jets aswell and all unmarked so basically useless. I have replaced the primary with an OKO 40. I have 2 Hex OKO mains to try (102 & 105) but with the copy main jet holder it is too long and the hex jet wont allow the bowl to go back on. So I am sourcing an OKO main jet holder now. The port thing for the scooter will be blocked off. I may experiment with it later if I can get the carby dialled in.
 

my67xr

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i have played around with a few of both Taiwan and China OKO's.

the china OKO's have a slightly larger Slide compared to the Taiwan OKOs.
probably due to them copying the OKO Slide dimensions, then having them chrome plated.
the china slides are 16.4mm deep, and 29.94mm wide, compared to the Taiwan OKOs' slide 15.78mm deep, and 29.84mm wide


nah, it is still a power jet though.
how it works is it forces extra air into the bowl at higher rpms and creates a higher pressure, so it forces more fuel out and richens the mixture.
generally you use a Main Jet 10%-15% smaller than an OKO without a power jet

Scooter Assassins / dragonparts0204 on ebay sell a heap of OKO spares cheap
they don't have a Main Jet Holder or a Jet Block listed atm, but i'm sure they sell them just ask them if they can list it for you.
don't forget to get a new gasket for it too

also another thing to do to the chinese OKO is to slightly enlarge the cutaway where the drain plug screws into the fuel bowl.
so you dont have to take the whole bowl off to swap the Pilot Jets over.
it only needs 1 mm filed out on the outer edge of the cutaway, but don't go too far as the plug won't seal properly.
 

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