Kehin PWK 28mm vs OKO 28mm. Inside?

Discussion in 'Carburetor' started by Knowpig, Dec 23, 2009.

  1. Knowpig

    Knowpig New Member

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    OK, I know you get what you pay for.
    But I am wondering if anyone has stripped down a PWK 28mm Keihin and OKO 28mm to look at the internals side by side. I am VERY curious as to what is physically different about them.
    Does the needle have a different taper on the PWK?
    Does the jet tube have a larger or smaller ID on the PWK?
    Does the slide have a slightly different cutaway?
    All of the above/none of the above?
    I am beating my head against the wall trying to get this little OKO just right.
    And it's pretty close, but I want it better. I am getting to the point that I think I may need to break down and just buy a Keihin.
    After our Glamis trip, we are now at a 48 pilot (and I think it wants a 45 or 42). The drop from a 50 to 48 pilot got us a much better idle. Still 2.5 turns out, but had to turn the idle screw down a bit.
    We are still on the first clip on the needle. And if I had a leaner needle, it would go in. It wants less needle at lower throttle and I think maybe just a hair richer taper a little deeper into the throttle.
    And we are running a 172 main. Yup. 172. And she likes it. I didn't have a 170, but the 172 is pretty happy.
    So what the heck am I missing?
    Can I just buy a PWK needle or maybe a PWK jet tube and throw it in the OKO carb or am I beating a dead horse trying to make chicken salad out of chicken $h!t?
    And we are running VP110 pump fuel mixxed 4 gal VP/ 1 gal 91 pump shell gas. Oil at 32:1 Maxima SuperM.
  2. foolish913

    foolish913 New Member

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    the oko should use the same needle an jets as the keihin mine does an the only diffrence is you is a lil smaller
  3. Knowpig

    Knowpig New Member

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    Foolish-
    Yes, the jets and the needle are interchangeable.
    What I am asking is what is the difference between the stock OKO vs. stock PWK needle (taper/shape) and on the jet tube (screws in from the underside of the carb, also called an emulsification tube) is there a difference in length and/or inside diameter?

    Anyone?
    Anyone at all?
  4. pittboss45

    pittboss45 New Member

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    First off, what compression is the motor at right now. I assume that you are running an open airbox not a clamp on filter.

    What all has been done to the motor?
  5. Knowpig

    Knowpig New Member

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    2 over Wiesco piston, FLOTEK aggressive trail port and head mod, Boysen reeds, FMF Fatty pipe, 28mm OKO carb, +4 timing mod, 14t front sprocket.
    I have not put a gauge on it to measure compression, but it was set up for pump fuel. I run the race mix to keep it cool as we work it pretty hard in the dunes. For what it is worth, the head had some taken off it for sure and has a much better shape to the dome. And it takes some more to kick it for sure. Feels good! And the filter is this..................
    [​IMG]
  6. ROCKSTAR

    ROCKSTAR New Member

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    not sure on teh different needles, but if you are having jetting problems, this may sounds crazy, but after looking at your mods.....try a leak down test. sometimes an air leak will cause jetting issues....
  7. Knowpig

    Knowpig New Member

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    I agree that an air leak could cause an issue, but in this case I am fat down low. Not lean. I would think an air leak would give me lean issues.
    I am going to try to hunt down a different needle, I think.
  8. 370

    370 New Member

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    chaning the needle taper will effect youir from abouit 1/4 to about 3/4 throttle. if thats where youir issue is then changing that taper by swapping needles is a ver common prcatice.. thats why keihn makes a ton of different needles. what needle is in that carb right now? i know the oko and the PWK's are about identical from as much as i've looked at them.. i have the PWKS and rockstar has the okos.. my advice woudl eb find the needle you ahve and then google the keihn needle chart and start your selection from there.
  9. ROCKSTAR

    ROCKSTAR New Member

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    well, that kills that idea.....air leak would make it lean out....must not have caught that....

    but all in all, wouldnt be such a bad idea.....

    370 is a kehin man. he can find info quick....he knows where to go....
  10. Knowpig

    Knowpig New Member

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    Yeah, I have the needle chart. I will have to look, but I'm pretty sure the OKO does not have any markings on the needle. I can also tell you that the 48 pilot was a much better idle than the 50, but I am still 2.5 turns out for best idle. I have a 45 and 42 to try out. If the smaller pilot helps enough, I guess I might be able to get it to go on the 2nd clip on the needle. That might also make it come together. Like I said, it's pretty happy, I just want it to be extra specially happy.
  11. Knowpig

    Knowpig New Member

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    I just wanted to post a little update............................
    The OKO needles are blank-no stamping. So it's a "what I got" needle.
    But the needle may not be the issue after all.
    I started with a 50 pilot, then dropped to a 48. And it did improve the idle. And in reading Keihin charts and reading posts from this and other forums, I started to wonder if an over rich pilot could be causing me to use the needle to try to correct it. So I threw in a 42 pilot and bumped the needle a clip or two. I went to the 4th clip and it started to lose performance so I backed it down to the third clip. I left the 172 main in the whole time. I figured since I was now on the 3rd clip, maybe it would like a little less main jet. So I put in a 168 main. I couldn't believe it. It didn't want to rev out. Just sputtered until I backed out of the throttle a little. So I threw the 172 main back in and it was revving like right now! So I went out and bought a 175 main and put THAT in there. Seems pretty happy now. I am heading out to Glamis again this weekend for New Year's. So we'll pop a new plug in there and see what kind of coloring the 175 main gives us. It just seems to like it when I fatten her up now. I'll post some video and let you guys know where we ended up after the New Year!
    royalt67 likes this.
  12. royalt67

    royalt67 New Member

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    Thanks for the update, Pig. Mine has never had good color, just shades of grey before it goes black, depending on what main I use. Runs good, just never a brown plug. +5 rep
  13. Knowpig

    Knowpig New Member

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    I appreciate the info.
    We ended up getting hit pretty hard by swine flu and didn't get to make our trip for New Year's.
    The older boy went down Sunday after Christmas, then Monday night around midnight the 12yr old got hit hard. About an hour after that my wife got dizzy and couldn't stand. Then around 3am I got hit. By Tuesday morning, my 12yr old could not stand. We got him to the urgent care and ho took 2 bags of IV fluids. All in all, it took us almost a full week to get back on our feet. I've never had anything hit us so hard so quick and effect all of us. Just glad we got through it.
    Hopefully we will be able to get that little Blaster back in the sand by the end of the month to see how she does. I think I might have a vid of it before this most recent jetting round from our last trip. I'll see. But thanks again to everyone for the help.
  14. Knowpig

    Knowpig New Member

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    I put a vid up in the photo/vid section.
  15. phragle

    phragle Member

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    First...get rid of the k&n before you need a new crank. you really dont have that much motor and a 28mm carb. the stock airbox and boot is capable of flowing a great deal more air. OMHO, go back to a stock type airbox or a 250r one, either without lid and ,move up to a 34mm carb. then invest in an EGT and use it for setup.
  16. samolia

    samolia New Member

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    wouldnt a wide range O2 sensor work too??
    and then just check for your air/fuel mixture levels untill your in the perfect zone

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