400ex carb on 300ex

[01_300ex]

what do you all thing of a 400ex carb on a 300ex. Would it work good with a 11:1 comp. piston, or would it over carburate or something.

[R-Crazy]

i dont know, but i have thought about it. how many mm. are they?

dave

[01_300ex]

i think like a 35mm.

[NVR2L8]

Installing my unused 400EX carb on my wife's 300EX is a project I've been meaning to get to, but haven't for several reasons (mostly getting the time). Anyway, from what I've read the 300EX responds very well to the larger carb, and will work fine on a 300EX with just minor intake and exhaust mods, to one that has been heavily modified. BTW, the stock 300EX carb is 32mm, while the 400EX carb is 35.5mm. Also, although the side mating to the intake manifold (engine side) is the same size, you'll need to replace the intake boot with one for a 350X, as the 400EX carb intake inlet (airbox side) is larger.

[R-Crazy]

would i have to do any other mods to it to get it to equalize. maybe open the air box with outerwears?

dave

[NVR2L8]

Well, I'm not an engine expert by any means, but if you run a 400EX carb on a 300EX with a free-flowing exhaust and air filter, I don't think you're going to have any problems as long as you correctly jet the 400EX carb for your machine. I also don't think going from a 32 to 35.5mm carb is "that large" of a jump where you have way too much carb for the 300EX engine. Also, running with no airbox lid or an outerwear would help get max flow, but the key to using the 400EX carb, is to dial in the carb once it's installed on your machine.

BTW, the one person I ran into quite some time ago who had a 400EX carb on his 300EX, was running a stock engine with a complete Supertrapp headpipe and silencer combo, along with a stock air filter (might have been a UNI) with about 6 one inch holes in the airbox lid. Although I didn't ride it, from what he told me throttle response was much snappier, and it pulled a little harder throughout the powerband. For what it's worth, I'd have to say the 300EX in stock form could probably benefit from a slightly larger carb...especially if you can pick up a used/cheap 400EX carb...but just don't expect it to provide massive power gains.

I used a stock 400EX carb on my 330EX all last year with no problems. The carb will bolt directly onto the engine with no mods, but works better if you use a breather tube from a 350X three wheeler and install that between the carb and airbox. You can get a 350X breather tube from Service Honda for around $15 bucks. A new 400EX carb is around $165, or search Ebay for a used one.



Chris - D23 #66
2002 Laeger's/AXIS 365X MX racer
2000 Honda/TC/AXIS 330EX XC racer
See ya at the races........

ive seen the 400 carb on many 300s and even with just a piston and cam or with the big bore, it runs awesome....bolts right on with no mods, so pretty good way to step your bike up



ill be happy to sell mine for 100 dollars plus shipping which wont be but a few dollars probably.....i got an fcr and really dont need it anymore.....its like new and is off a 2001 400ex....just thought i would let you know....

[305exracer11]

ive got a 38mm carb on my 305ex it really does alot


1997 305ex
+4 axle
+2 arms
18 turf tamers
tag handlebars
works shocks
ac nerfs and grap bar
duncan front bumper
ceet ghaphics
web cam
hard rocker arms
strong valve springs
14t counter
39t in the back
kn filter
shaved plastic
denton steering damper
pro design kill switch

[xe003rider]

do i need the whole boot from a 350x or what in not following 100% thanks