Yoshimura carburetor sizing for takegawa 4v

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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; Ive got a 88cc sohc 4v coming from takegawa and I have been looking at yoshi carbs to go with it.. Yoshimura just got some ...

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    radcorynw's Avatar

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    Yoshimura carburetor sizing for takegawa 4v

    Ive got a 88cc sohc 4v coming from takegawa and I have been looking at yoshi carbs to go with it.. Yoshimura just got some stuff in stock YD MJN24 is in stock and I was about to order it but I am wondering if I should wait for the 28mm version to come in stock instead. I know this tak head will have loads more flow going through than my 88ccTB head I'm on now. Would I see any benefit with the larger version of the carb? Or is the 28mm too open for the 88cc?

    I mostly run mid to high range rpm on road. but am still trying to build the motor with a balanced power band not just for top end.. this is why I decided to just ask others what they think would be the best choice carb to go with the new setup and why..
    thanks

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    Mahinsminis's Avatar

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    I think the 28mm is a bit big for 88cc. I run a 28mm on my 190cc 4v.

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    At first thats what i thought until I read more about the Multi jet nozzle thing yoshimura does and it got me thinking their carbs were larger bore because of that or something. I only have a 22mm on my current setup so the 24mm already seems like a step up.
    Anyways I just ordered the 24mm
    Still down to hear opinions though

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    Matthonda86's Avatar

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    the 28mm would give you more top end but your wanting more of a balanced engine/power so i would go with the smaller carb to help with the balance of power.
    Sometimes I go fast, but most of the time I just think about it.

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    Hi
    I put my nickel in {20 cents in OZ}
    I am running a 26mm Yosi on my XR75 Honda with a 120cc capacity 115 octane fuel and big SR35 takei cam
    when I first fired it up, carby run great the fuel atomization due to the modified Yosi needle is great
    but first test ride running to lean and had to go up a couple of jet sizes and play with the needle until I got the right A/F ratio on my 5 gas machine
    but the others guys are right depends on what balance you want 24mm will be better for thru the range power
    bigger carb,if you have big duration cam,high comp piston,port work ect, and want to keep it at high RPM most the time

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    silvjorr's Avatar

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    Here is an old thread about Yoshi carbs, hope it helps a little: Yoshimura TM-MJN24 Carb

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    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.

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    From the tm-mjn 24 there are actually three versions. One for 88cc, one for the 88yosh kit and one for more than 88cc.

    (Hopefully coming summer I have a driver with the 88yosh setup. So far gathered an ab27e, tak oil pump and 3-plate clutch, the full yosh 88 kit and the tmjn24 for that specific setup. Now I need time and temperature to build the engine... (and get the gorilla motor plated))

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    I actually ordered the YD model and don't think I've seen the YD MJN in 22mm... 22mm is what I am on now with 88cc. Im all for better response at first I was thinking 24 would be big. It was their multi nozzle thing that made me think response issues wouldn't be noticeable if not improved.

    ^then fatcaaat says he's putting a 22mm on 127cc?... maybe i should have looked through webike a bit more for a 22mm model. I kind of wanted to order within the states though.

    my gearing now is about all the motor can pull so its not easy to stay in the super high rpm range all the time with its current 22mm mikuni and TB 88cc

    good info guys
    Last edited by radcorynw; 02-10-2015 at 01:02 PM.

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    So they make a vm22 or you mean the flange mount mikuni 22 carb that comes on most bikes or with most engine kits?
    Reason I ask is that this carb below works very good on my 125 engine.
    From cold start, sto n go, steady cruise and wide open, it's a great all around carb.
    I do have a free flowing exhaust also though.
    I may try it on my 150 engine also.

    Mikuni 22mm Carb - WHS-0957 - CARBS and JETS - Pit Bike Engine Parts - TBolt USA, LLC
    Hidden Content Toooooo many mini bikes
    84z50, 91z50r, 95z50r, 91 & 99z50r apart, xr50, 2-xr70s, 03xr100, 08 hayabusa
    1999 & 2000 Jincheng Pandas stock n street legal....
    2 - 2013 skyteam flashback Red & black
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    ^that carb is kind of like the one i am running now.

    I just found some things out. I got the yd24 for standard Grom so if I want more response with 88cc i can get the multi jet nozzle set which has a nozzle designed for yosh 88cc head.. I'm sure it works for any 88cc. But I'm gonna run it how it comes on my TB head and go from there.

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    fatcaaat's Avatar

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    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?

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    nielspbr's Avatar

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    Running a vm26 on my daytona 150, runs like a champ. (advised by daytona, pe28 )

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    DSR BLACK DEATH's Avatar

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    Why not keep the 22 carb on it?
    Its a good all around carb
    Hidden Content Toooooo many mini bikes
    84z50, 91z50r, 95z50r, 91 & 99z50r apart, xr50, 2-xr70s, 03xr100, 08 hayabusa
    1999 & 2000 Jincheng Pandas stock n street legal....
    2 - 2013 skyteam flashback Red & black
    2-71 ct70s

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    my mikuni carb is fine and it will be staying with my TB head whatever other bike that ends up on. reason I'm upgrading carb is for responsiveness mostly I just thought with a 4v from takegawa a larger carb MIGHT have an advantage. but 24mm already IS large as confirmed by most opinions in here

    Im wondering now if my new engine would perform better with the TM MJN 22 over the YD MJN 24.. Part of the reason I chose YD was downdraft and short manifold. It just doesn't come smaller than 24mm. either way I'm stoked it will be here thursday.

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