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Discussion Starter · #1 ·
Sredrum (Chris) over on YFZtech has the FCR carb boring wired. General concenses over at KTM Talk is that the FIRST mod on a 525 should be a 41mm carb

this is the link to Sredrums section on YFZtech.

FCR carb boring

The stock 39mm can be taken out to 41mm easy enough, to go larger you will need a new central section insert, Sredrum has these for 43mm and 44mm. Apparently DASA also makes a 43mm central insert

43 and 44mm central sections
 

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check out a 07 crf FCR carb. i had one on my Honda. it was taper bored to 43mm by DRG. well worth the money.
 

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the new centre sections are $75..... if I could get a whole 41mm carb for less I'd go that way ....... watched 41mmm carbs on ebay recently going for 400 - 500 range.....
 

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that crf carb goes for $425 from service honda
 

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the new centre sections are ..... if I could get a whole 41mm carb for less I'd go that way ....... watched 41mmm carbs on ebay recently going for 400 - 500 range.....
Hey Kiwi

PM me your addy and I'll send you that aftermarket 43mm venturi insert ok.


I have my 41mm MX bored to 43.5mm without need for a new ring.
I highly recommend you measure your carbs ID @ the venturi if you have the measuring tools. I know for a FACT you can machine the stock venturi to 43mm or bigger. The stock venturi is'nt even 43mm wide at thats at the outside of the insert. Not trying to talk smack to you,just want to make sure you understand B4 telling guys there stock carbs can be bored to 43.5mm with the stock venturi.

And just so KTM owners know up front there FCR's are a very good model. And can be bored up to 44mm if they want it. CRF/TRX are thinner at the bodies and the max I'll go with them is 43.5. Only the YFZ and KTM FCR's make good carbs for true 44mm

But I'll be the first to say 42mm and 43mm will work great I'm sure. Remember,if you go with a big FCR you better have that head ported or it will act like a bottleneck at the heads opening into the intake port.

Here's some pic's

Drilled and tapped the KTM bowl so a leak jet can be used
The next four pictures below are a KTM FCR taper bored to 42mm





Here's two aftermarket venturi's. Left is 44mm and the right is 43mm
 
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