anybody run the 400ex carb on their 300ex?

[JDiablo]

just wondering if anybody runs this,and what power gains could i expect if any and is it worth the money?

[ghak99]

I run a 400ex carb on my 250x. I am still getting the jetting worked out, but it has alot more throttle responce then the 250x carb had. It seems to have more top end even though my jetting is still a little wrong, once i get it right it will be much better than stock carb. I do have the choke removed from mine though.

[JDiablo]

i could use the throttle response because mine sux....and i guess some top end,but i prefer bottom end for XC...sounds good to be then,i gotta go through with the guy on the deal then

[ghak99]

By your mods it looks like your are in need of a cam. Are you running a stock cam?

[JDiablo]

Originally posted by ghak99
By your mods it looks like your are in need of a cam. Are you running a stock cam?


if your talking to me yes i am running a stock cam,everything in my motor is stock,is it hard to put in a cam?do you have one you want to sell?

[ghak99]

No I don't have one to sell,I am just saying a cam would really wake your 300 up. They are easy to put in, but if you are going to tear it apart, you might as well go with a piston and cam combination while you are in there.

[JDiablo]

well the stupid *** guy at my local dealer said there really isn't a need for motor work and now my dad is like that is just a waste of money,i mean i would do it myself.....but i do everything except motors.....and forget about the piston...ill just end up screwing up my whole motor just because i needed to try and put a piston and cam in...grrr stupid guy...he owns a banshee so go figure

[dirtmomma]

I just picked up a 400 carb & can't wait to get it :blah: YES ghak, I'm thinkin' on a cam ;) I really wish we would of did it when we had it tore apart to do the piston but it's always that LACK of green stuff that gets in the way LOL may have to check on some prices here soon!! Then again we may be tearin it down soon again anyway to put a BIGGER piston in it so then I would def need a cam :blah:

[ghak99]

I just put mine together a while ago, and already wish i would have went with a big bore. O'well, after +3 a arms and a sway bar that is the next step.....a very large big bore:D I went with a web cams cam and can say it worked great.


Lmao...I just spent 300 dollars so I had better quit talking before i get any more ideas.

[JDiablo]

how much better is it with the cam?how much of a noticeable(sp) is there with the cam in>?

[dirtmomma]

Originally posted by ghak99
I just put mine together a while ago, and already wish i would have went with a big bore. O'well, after +3 a arms and a sway bar that is the next step.....a very large big bore:D I went with a web cams cam and can say it worked great.


Lmao...I just spent 300 dollars so I had better quit talking before i get any more ideas.


I'm in the same boat as you, just did my piston & rings went w/ a 75.5mm just in Oct. & wanted a big bore about 3 races later:rolleyes: We're thinking of trying to put my hubby's stock 400 sleeve in it :blah: my brother in law has his wheels turning LOL I dont' know what that would make it but it sounded good to me!!! We're getting ready to do a 440 in our 400 & so we'll have the extra sleeve. We'll have to see if it'll work!!!

[ghak99]

I went with a 12:1 piston, carb, pipe, cam, rockers, valves, springs, port and polish and other stuff all at the same time so I really don't know what the cam did by itself.

[JDiablo]

OoO,how much was the port and polish?

[ghak99]

I did it myself....which went against all advice recieved from others on this site.


I have been through an automotive training program, and had a basic understanding of aiflow to and from a cylinder so I just did it and made the ports as smooth as glass when I was done. It seems to have woked out.

[Out_Sider]

im running a 400ex carb...and it did give some throttle response, but im gonna get an edelbrock when the proper time comes for it. but the port/polish i want is like 240 or somin..but the one I want is 350

[Pvt. Maggot]

i'm thinking about it...i have a 20 over 11:1 high compression piston...prob getting a tc cam...and a T-4 shorty with bigger headpipe...think i should? don't you need the 350x air boot?

[JDiablo]

yea you need the 350x airboot,but ye if your low on money this would be a ideal carb to use instead of getting a aftermarket one

[ghak99]

The 350x boot goes on the carb much easier. I boiled the end of mine and then fitted it to the carb, and now it works great! Some use the stock carb boot, but I have no clue how they get it on the 400ex carb.

[dirtmomma]

OOOO dont' have a 350x boot BUT we did an awful good job of mdifying one for the blaster to take a 34 mm carb :D it's pretty easy to make one, well I should say it was for the blaster LOL

[speedy400]

If anyone needs a stocker 400ex carb. I have one for sale, make me an offer, it might come with dynojet kit, not sure yet, PM me if intrested. -darren