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View Full Version : 39mm carb on a 95 trx,yeah,or nea?


3leggeddog
07-15-2007, 07:23 PM
is this a good idea?i got a new fcr 39mm race carb,but don't esnt to choke the bike down.obviuosly i want better performance.this carb really worked well for my 400,but will it hurt the 450r?
3leggeddog
07-19-2007, 08:24 PM
come on guys any input here????
KFX440ROX
07-20-2007, 07:01 AM
well the stock carb. is a Keihin 42mm so i would think going to a smaller carb. wouldn't be good but idk. The FCR 39 carb. i had on my 400 had a accelerator pump which was pretty cool and my 400 was a beefed up 440 and that carb. handled it fine but IMO i would just keep the stock 42mm carb.
Chino886
07-20-2007, 07:56 AM
39 will work fine, but punch it out to a 41 mm or larger and that will be the ticket.

FYI CRF450s have the FCRs are basically the same motor! 06s and up came with 40mm FCRs.
KFX440ROX
07-20-2007, 08:00 AM
Do you know why they went to a smaller carb. on the 06 and up?
Chino886
07-20-2007, 08:03 AM
Originally posted by KFX440ROX
Do you know why they went to a smaller carb. on the 06 and up?

Yes, the FCR is a far superior design than the 42mm round slide on the 04/05 bikes. Throttle response and flow are drastically different on the 2 carbs.
GPracer2500
07-20-2007, 10:22 AM
What he ^^ said.

You can't really compare the numbers attached to the "size" of two carbs when they are two completely different carbs. It's apples to oranges. It's almost like saying: Well, this utility quad has a 500cc engine so it must be faster than this 450cc sport quad. That's sort of an exaggerated analogy--but you get my point.

Take a look. 39mm FCR from a YFZ on the left and 04/05 TRX450R 42mm Keihin on the right.

http://img231.imageshack.us/img231/3055/carbs450ryfzdf6.jpg
[image courtesy of Buck]

And even if the FCR did actually have a smaller "suck-hole" :p (which it does not appear to have), that still wouldn't be the last word on the potential flow. The FCR doesn't have a round slide or butterfly getting in the way like the stock 04/05 carb does. You've got to look at the overall picture--not just focus on one particular number.
3leggeddog
07-21-2007, 07:47 AM
somit may be an ok idea?
Chino886
07-21-2007, 09:42 AM
Originally posted by 3leggeddog
somit may be an ok idea?

It's a great idea!:devil:
3leggeddog
07-21-2007, 05:05 PM
how do i get it to fit?does anyone make a adapter kit?can i just get like a yfz intake boot?both the head side,and air box side rubber boots are too large.any suggestions on getting around this?

does anyone want to buy this 39mm fcr?i would also trade it for some front hyper beadlocks
GPracer2500
07-21-2007, 06:31 PM
NOSS Machine makes an adapter for fitting CRF450R FCR's to TRX's.