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Yoshimura carburetor sizing for takegawa 4v

This is a discussion on Yoshimura carburetor sizing for takegawa 4v within the Z50, CT70 and JDM Monkeybikes forums, part of the General Talk category; Cool let us know how it works out...

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Thread: Yoshimura carburetor sizing for takegawa 4v

  1. #16
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    Cool let us know how it works out
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    Quote Originally Posted by fatcaaat View Post
    Here it is....
    YOSHIMURA : Mikuni TM-MJN22 Carburetor Kit [770-404-2000]

    And it arrived on my doorstep today. I simply do not agree with takegawa or yoshi on carb sizing. I used to think that bigger was better...until i started my own experment. And why Takegawa provides a VM26 with their 88 +r kits is beyond my comprehension. I had a vm26 on top of a well built 108 at one point...and it was a 65mph bike but ran like crap off throttle and had poor response. After installing a mikuni VM20 on it instead, it cleared everything up and I lost no top speed at all.

    At some point we lost all sense around what carbs should be on these pitbikes. People are installing 32mm pumper carbs on sub 200cc bikes. My Norton Commando uses a mikuni VM34 at 750cc. My Vintage enfield at 500 cc uses a 28mm. I understand that the factory makes an attempt to balance drivability and emissions with their setups, but everything needs to work in harmony here.

    Let's use a ratio just to explain the absurdity for a second:
    Stock 70 = 16mm carb
    Race prepped 88 = 24mm

    Keeping with singles then...

    What would a race prepped crf150 need?38mm?
    What about a race prepped CBR250? 46mm?
    the thing you are not addressing in all this is how great the volume of air each engine is consuming. An 88 cc engine may not be overly large in displacement, but if it's speed (rpm ) and volumetric efficiency is greater than that of the 500 cc Enfield then it will need a larger carburettor to be able to supply enough air and fuel to have it run at its highest potential. So given that the volumetric efficiency is the same in both engines, which it won't because the 88 has later and better design, the 88 @ 13,000 rpm will consume just over a third of the air of a 500 cc Enfield @ 6,000rpm, but it has less than half the time to do it, so you will need to have a bigger inlet to do so, so the carburettor for the 88 will seem disproportionately bigger than the one on the 500 cc .
    From the engines you have described that you have tuned yourself I would guess that not many are running at 13,000 to 14,000 rpm in top gear - which is what a Takegawa 88 or 106 with a Super head + R will do

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    Has anybody ran the YD24mjn carb on an 88cc? or even a TM24? I think I'm going to be doing some jetting changes and or a nozzle change on mine and was wondering what other people have done with these carbs on 88cc's.
    mine is the GROM carb kit version tuned for 125cc. tuned to my ability she runs, just not right.

    Also, does anyone know if the jets and nozzles from YD series and TM series (24mm and 28mm) are interchangeable?
    Last edited by radcorynw; 02-16-2015 at 11:54 PM.

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    Does anyone know if the multi jet nozzles from the TM line of carbs will fit the YD line just the same?

    Also are they interchangeable between bore? like 22 to 24mm etc..

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    Quote Originally Posted by radcorynw View Post
    Does anyone know if the multi jet nozzles from the TM line of carbs will fit the YD line just the same?

    Also are they interchangeable between bore? like 22 to 24mm etc..
    TM and YD metering nozzles are different - the YD has no adjustment to raise or lower like the TM does, this in my experience makes the YD less user friendly and hard to tune in some cases.

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    raise or lower the nozzle? i thought it stayed in position and just the slide moved? (at least thats what my YD looks to be doing)

    I put the order in on webike for the rest of the parts ill need to finish including main and slow jet sets and the nozzle meant for 88cc (YD version). Until then I'm putting the old mikuni back on. and waiting..... haha

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    He meant the nozzle, normally there is a needle in the slide but yoshimura uses a hollow needle with holes/nozzles.

    Last edited by nielspbr; 02-19-2015 at 04:54 PM.

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    i understand the nozzle. but mine does not have a height adjustment like a typical needle and i guess the TM versions.

    parts are on backorder from webike until april... It'll be spring once the 4v and yd24 make in on my bike now.

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    Quote Originally Posted by fatcaaat View Post
    Having run both versions at 26 and 24 on different motor combos ranging from 146cc to 124cc, I'm going to say that a 24mm version is going to be pushing the too big limit on an 88. I don't really get why people think adding a huge carb increases power...it does...but only at like 8k+ so if you are running your motor ragged over 8k 90% of the time, then sure, a bigger carb is going to be great.

    Here's a direct compare that I did at one point:
    Motor was a Chinese Lifan midblock, bored and stroked to 157cc. had cam and portwork too...75mph+ motor.

    I didn't write all this down, but i tried the following carbs on it. TM28 flatslide, VM26, TM24 flatslide, TM26 Yoshi, knockoff VM26, and a VM22. When they were all properly jetted, the TM28 gave the highest top speed...by like 1-2mph, but hands down the most drivable was the VM22. Off throttle torque and midrange was better than all other carbs. It produced the lowest top speed (about 4mph less) but seeing that the majority of my riding was in the 50mph range, it frankly didn't matter. Tunability was more important.

    So, when choosing a new MJN carb for a 127cc Nice 4v+r, which is currently in shipment from webike, you know what I chose? the 22mm version.
    Been on the fence with these. Thinking of running one my 108 TB V2 head engine. Yoshi TM24. Now you got me thinking 22mm! I am the same way. I want easy tuning and all around performance. Not just flat out. Couple of MPH's off the top end no big thing. What do you think Fatcaat for my 108 V2 Head. You got the experience with these. Also how did it perform "out of the box". Need extra main jets/pilot jet to get it right? Thanks! Hey why don't you come up to Windber again this year!
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    Quote Originally Posted by RAZZO View Post
    Been on the fence with these. Thinking of running one my 108 TB V2 head engine. Yoshi TM24. Now you got me thinking 22mm! I am the same way. I want easy tuning and all around performance. Not just flat out. Couple of MPH's off the top end no big thing. What do you think Fatcaat for my 108 V2 Head. You got the experience with these. Also how did it perform "out of the box". Need extra main jets/pilot jet to get it right? Thanks! Hey why don't you come up to Windber again this year!
    I am going to be running a MJN22 on a stock honda nice engine (with a little port cleanup). I think that is plenty big. I also think that a 22 will be perfectly suited for the engine you are describing. Out of the box, the jetting was off quite a bit. You can get all the jets you need from niche cycle for this carb...sure you can get them elsewhere too. I currently am running a vm20 on a tb108 kit (non rocker head) and it really is perfect for that motor. I also had a vm20 on top of a similar 108 setup. This one ran the tb stroker and the tb v2 piston on it but the head is a honda nice that was worked heavily running same valves as the v2 head (so pretty much the same minus the rockers).

    As for Windber, unless something else is in the way, I do plan on coming up.
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    Excellent! Thanks for the quick response. I'm running a TB 20mm 92 main/38 pilot on it now with zero problems. For inexpensive carb they are great. Never a problem dialing one in and stays put.

    What jets come stock in the VM22? What do you think I'll need? Bigger main and pilots? Thank you for the tech tips on these!! Glad to hear you are going to make it to Windber!
    Last edited by RAZZO; 03-03-2016 at 03:44 PM.
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    Quote Originally Posted by RAZZO View Post
    Excellent! Thanks for the quick response. What jets come stock in the VM22? What do you think I'll need? Bigger main and pilots? Thank you for the tech tips on these!! Glad to hear you are going to make it to Windber!
    I think you meant the MNJ22? The pilots are your garden variety pilots but they run the big mikuni round that no other carb we run on mini's runs. I got 5 sizes up and think I landed in the middle. I forget what it comes with...if i get out to teh garage I'll look as I have the stock one sitting here waiting for my Nice to arrive.

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    Yes the carb I'm looking at is Yoshi/Mikuni -

    MIKUNI TM-MJN22 Carburetor Kit by YOSHIMURA
    MODEL : 770-404-2000



    Please select the type for Yoshimura Head Kit Other Brand Head 124cc for Monkey
    Price: 299.19 USD (34,000 yen)
    Last edited by RAZZO; 03-03-2016 at 03:54 PM.
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    I just bought a TM-MJN24, but havent run it yet. Yoshimura recommends the TM24 or 26 on THEIR 88 head/cylinder which is what I have. I felt the 26 was gonna be way too big, and even the 24 I think is big, but thats what they suggest so I went with it. Its going into a ZB, so hopefully it'll be alright.

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    Prices have gone up...i got that kit for 250 when the yen was at its worst against the dollar and it was a little cheaper.

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