400ex carb on 300ex

I was wondering what modifications i would need to mount a 400EX carb on my 300EX. I heard that I will need a 350X air boot, what else do I need? Thanks

[ChadEXer]

I got a friend wantin to know the same thing!

[max400EX]

Some one should know...

[PDunes300ex]

Are there any noticeable power gains by simply putting on a 400 carb. I know its bigger but is it worth it?

You definitely need the 350x airboot. I tried to install my 400ex carb on my 300ex today and realized that it wasn't going to fit, so I just ordered the airboot from servicehonda.com. All you have to do is take the throttle cable out of the old carburetor and into the new one. It really isn't that hard, once you figure out how to do it (I experienced this today and was so proud of myself). I can't wait to get it on...but then the dreadful jetting comes.

[Red Rooster]

I want to get a carb so bad but my funds are being reserved for a truck. Let me know what kind of gain you get when you put it on. quadfamily also did this (not shure if he got it on yet) but you can ask him for info too.

[max400EX]

bump

[01_300ex]

I didnt do anything to the 400ex carb, but put it on. You DONT need a 350x airboot, but the 300ex airboot comes off of the carb if you hit jumps and stufff like that. So i would get a 350x airboot.

[max400EX]

Thanks 01_300EX... 01300EX is my friend and hes not very good with motors and needs all the help and power he can get. What kinda jets are you guys running with pipes and air box mods on the 400EX carb?

[max400EX]

bump

[01_300ex]

im running a 160 main jet, with the mods i have in my signature.But i need to go up one or two sizes more, because it backfires when i let off of the throttle.

[ride300exred]

I was wondering the same thing what are you running for your needle,clip and you pilot jet 01 300ex? I will probraly be running almost the same setup on mine soon.
Thanks Kris
Also Are you running 350x airboot.

[01_300ex]

i just have the stock 400 needle clip and pilot jet. I dont have the 350x airboot on yet. How much does the airboot cost at service honda.

[250rampage]

im running a 160 main jet, with the mods i have in my signature.But i need to go up one or two sizes more, because it backfires when i let off of the throttle.

Don't go up on the jet, lean it out some. A backfire is when unburnt exhaust gasses combust inside the exhaust pipe. Running rich causes excess unburnt gas.

[300ex4wheel]

So do you have to do any other major changes besides airbox boot. Is the a big power difference at all. Is it worth buying a carb to do it. I am planning on borring mine .060 over.

[pineway]

im putting a supertrapp ids2 full exhaust w/ kand n filter. also im running a 11.1 high comp piston stock bore. Does anyone know the jetting for this set up with the 400ex carb? Also what is the size of the 400ex carb?

[300ex mxracer]

the 400ex carb is 38 or 39mm

[heatatvracing]

i just put a 400ex carb on my 300 about 2-3 months ago, didnt have to change the boot or anything went right on. helped alot w/my motor, but do have quite a few mods so it really needed it.

[44oEX]

the 400ex carb is a 36mm

it`s a big power gain. you don`t need a 350x boot...you can make it work witht the stock boot just take a drill with a small gring rock and make the inside of the boot bigger...work great...start of with stock 400ex jetting (148) on a stock 300ex motor...for a modded motor go bigger