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I've been looking all over the web for information on the midbody of my keihin FCR MX39 carburetor, but I can't find much information.

I've seen rebuild kits, but I cannot find a diagram. I'm not sure that I need to rebuild the midbody but my carb is roughly 20 years old, and I think I my have damaged it when I cleaned it.

I recently cleaned it bye following instructions I found online and in my Yamaha survice manual (the carb is in an 03 YZ450F). I took apart the carb, the jets, the float, the slide, the excelerator pump, everything rubber that could be damaged bye carb cleaner, and I soaked it over night. I had no Idea that the midbody had gaskets that could be damaged bye this process though.

Has anyone rebuilt the midbody on keihin fcr or have a diagram that they could post. I don't want to tare into it without knowing what I'm doing first. 

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No diagram I have ever seen as it is not supposed to be taken apart. The trick to putting it back together is getting the right gasket, correct sealant (like Yamabond) and applying just enough sealant in the right places to seal it and not flow to block passage ways.

Solvents used have to be 'rubber safe' which excludes most common carb cleaners.

There are a couple of places that might be willing to tackle resolving your issue. James Dean Jetting, ZipTy or TokyoMods.

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I soaked that thing in heavy duty carb cleaner. I would'nt be surprised if the midbody seals are completely melted. It's super clean though.

That pbase.com link KRAYNIAL posted has some sweat pics of the midbody all torn down. It doesn't look to compicated.

I'm thinking I'm going to rebuild it before the weather gets good.

I appreciate the good information. Thanks yall!

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They do sell seals for the jet body here's one on ebay. Try looking around for one that fits your size carburetor.

 https://www.ebay.com/i/253414637640?chn=ps&ul_ref=https%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-117182-37290-0%2F2%3Fmpre%3Dhttps%253A%252F%252Fwww.ebay.com%252Fi%252F253414637640%253Fchn%253Dps%26itemid%3D253414637640%26targetid%3D539174539675%26device%3Dm%26adtype%3Dpla%26googleloc%3D1013701%26poi%3D%26campaignid%3D1669934864%26adgroupid%3D65058351099%26rlsatarget%3Dpla-539174539675%26abcId%3D1139336%26merchantid%3D101691151%26gclid%3DCj0KCQjw-tXlBRDWARIsAGYQAmcEFJBke3TxjcpU6l_m5FW6yonG-av-0wMpcA53JT6jcZIyAX5jY4waAtuhEALw_wcB%26srcrot%3D711-117182-37290-0%26rvr_id%3D1937259921436%26rvr_ts%3D29d82ff516a0ab1d3621fecbffab497a

 

It is from China, but I bought one and it worked perfectly fine. Best part is that it comes with a bundle of other parts. Some are questionable like the jets, ares they have no jetting number, and some of the slides are rough. But I just don't use the jets or slides, the needles are good though, the seals themselves are great. They do take a while to deliver though.

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all balls has proper seal kits for the fcr39, they have a good website where you can plug in your bike and find the parts part number 26-1512

after I did the mid-body on my 05 450x, the bike has run like a swiss watch ever since...

 

 

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4 hours ago, KRAYNIAL said:

DO NOT buy the above gaskets/seals. There have been multiple reports of them not fitting.

JD Jetting, Tokyo mods, Jetsrus.com all have what you need

Those people who bought them must've ordered the wrong size (there is an assortment of different sizes) . I have ordered 3 of these chinese kits from 3 different sellers, and ALL the gaskets and seals that came with them fit perfectly and worked great. They costed me less than 18 USD each. Since they are from China they did take a few weeks.

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46 minutes ago, Duke_Moto said:

Those people who bought them must've ordered the wrong size (there is an assortment of different sizes) . I have ordered 3 of these chinese kits from 3 different sellers, and ALL the gaskets and seals that came with them fit perfectly and worked great. They costed me less than 18 USD each. Since they are from China they did take a few weeks.

That is good to hear.  The FCR 40 kit was the issue noted on line. It was missing a gasket

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I just bought an allballs midbody kit for about $18 from: rockymountainatvmc.com

I'll let you all know if it works when it gets here.

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Posted (edited)

I put the all balls mid body seals in. They fit perfectly. The midbody was filthy, the passageways were gummed up, and the original seals were badly deteriorated. I cleaned and replaced the seals and now the carb is working great.

I definitely recommend the all balls for this carb. It came with all the seals, a wrench to take the tamper proof screws out, and replacement screws. Worth the money ?

Edited by Hefeweizen
Bad grammar
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On ‎6‎/‎16‎/‎2019 at 4:37 AM, Hefeweizen said:

I put the all balls mid body seals in. They fit perfectly. The midbody was filthy, the passageways were gummed up, and the original seals were badly deteriorated. I cleaned and replaced the seals and now the carb is working great.

I definitely recommend the all balls for this carb. It came with all the seals, a wrench to take the tamper proof screws out, and replacement screws. Worth the money ?

did you use any gasket sealant when you installed the mid-body gasket?

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1 hour ago, mattydavis said:

did you use any gasket sealant when you installed the mid-body gasket?

Nope.

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Posted (edited)

I rebuilt my FCR a few months ago as well, seals purchased from CRF's Only.

Did not use any sealant when re-assembling as after a few 'test fittings' it appeared to remain in place correctly when carefully aligning the mid-body.

Edited by mlatour
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