new fcr39 mx

Okay, I give up on the original carb on my 1998 WR400F. I clean it ,it runs ok for awhile ,then no idle  and hard start after it sits a week or two.


I am planning to buy a new  39FCRmx, with built in hot start, TPS and choke. Keihin claims this is the best ever  carb for 4 stroke dirt bikes.


MY question for you all is, has anybody here went with the new carb option? Was it worth the approx. $600.00?


Did you have any  trouble adapting it to your WR or YZ? From what I can see it needs an adaptor on the air box end and different throttle cables.


Thanks, Daniel

The later version of the FCR-MX as used on YZ450's from '05-'09 is a major improvement over the older FCR on the 400's.   Not sure where you found one for $600 new (they're about $950 from Yamaha, more or less bare), but they very well might be worth that.


I know several people who have installed used ones straight off of YZ450's and have said that it was the best thing they'd yet done to the bike, and that it would have been worth the price even if their original carb had been in perfect condition.  The improvement in starting, idle, and overall response is huge.


They typically go for around $200 used on eBay, and if you are patient, or can contact the seller, you can get them with the throttle cables (which you will need; they're different), and with the hot start, HS cable and lever. 


When installing to a 400, the one little quirk is that the carb is shorter front-to-back than the original.  To work around this, clamp the air boot onto the carb bell, then push it forward into the mounting sleeve and clamp it.

Thanks for the reply. I found several listings Sudco, Ebay, and PJ Motorsports, all between $580 to $620, for new carb       The carb has the hot start knob on the carb body like the choke, and TPS installed.


I am worried about a used carb because it could have problems and  I would be in the same  situation I am now. 

 The carb has the hot start knob on the carb body like the choke, and TPS installed.




That, then, is apt to be a "universal" carb that will be "ballpark" jetted.  You could end up fiddling with it for a while to dial in, but it will still probably be an improvement.   Still, I would pursue a used YZ450 carb, if not for the drop-in simplicity, for the money difference.

You should be able to find a YZ carb without any trouble. There are dozens of them from parted out bikes every week on ebay.

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