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carb ??
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Posted by: yz426ex36

I am trying to get a lil more power out of my girl friends 400ex.. it has a full system HMF exhaust,older stage 2 cam(getting replaced for the newer one) open airbox with a UNI filer, 416 bore, port and polish, rev box...

My ? is what carb should I install .. a 39 mm FCR off a dirt bike or my stock 05 TRX carb and why... thanks...

Posted by: zrpilot

yz426ex36,

IMHO I would run the '05 450R carb.

I had a Sudco 39MM FCR carb (slightly different then an OEM carb) and I thought it was a good carb. However I just could not get mine tuned good enough. It had a flat spot between 2-3K RPM that drove me nuts!

So, on the advice of Laz Sommers, I switched over to the 450R carb and it solved almost all my flat spot issues. Once I combined that with changing over to a Sparks exhaust, my flat spot virtually disappeared. I FELT the whole quad was much easier to ride and if I got down into that 3,000 RPM range, I could just throttle out of it!

Just my $.02 worth.

Your results will vary!

Posted by: yz426ex36

very good points...

lets hear some other opinions!!

Posted by: 2muchquad

I have no experience with the 450r carb but i can say the 39mm fcr made a HUGE difference on my 385ex.It was night and day,it revved much faster as if i had a lightened flywheel.Plus the throttle response was right now,which is sometimes more important than outright power.I have a 37mm fcr from a 250f i will try on my 400ex since i dont feel like raping the 39mm from my 385ex thats already tuned and set up.The fcr was way better than the 400ex carb on my 300ex i tried initially

Again i heard good things about the 450r carb but i havent came across one cheap enough to try for myself