400ex carb vs. 35mm FCR carb

[HondaRaceReady]

I searched and couldnt really find anything. The 400ex carb needs to be modified to work, right? On sparks racing . com it makes it sound like the 35mm FCR bolts right up and from what I know, FCR carbuerators add more power, right?

[XBLASTERRACERX]

The FCR is by far better then the 400ex carb by a mile. All top the 300ex racers are running between 35-38 fcr. As far as pricing goes it is really not worth the price unless u are truly out to win. So if u just want some extra power with out the price the 400ex carb is the best bet. Both carbs need work to fit the 300ex but if you buy the fcr through a company like sparks they will already do the modification for u. I'm not sure about the 400ex carb but if u need to know to know PM my friend 300ex#69j . where do u race in jersey?

[HondaRaceReady]

I dont race yet. I still need more practice. Hopefully next year.

[etondaddy]

Originally posted by HondaRaceReady
I dont race yet. I still need more practice. Hopefully next year.
We got a 400ex stock carb from eastcoast atv for like $150.00 new and it made a big differance. I had the intake horn of the 400ex carb machined down to fit the 300ex intake and bought a 400ex air intake duct and pieced the 300 and 400 air intake pieces together. But I was talking to Jody Bateman (Jb Racing) at Mapleshade and he told me if you buy a new 300 intake and air duct from Honda there new and soft and will mold to the carb or put the old ones in boiling water get them soft and but them on the 400 carb.

Mike Kozura

[QuadCobbler]

My neighbor gave me his old 400ex carb for FREE :D , he thought it was bad. The lid was bent on one side letting it suck air through the top. After I straightened it out, it works fine. I didn’t have to modify any thing to make it fit. The intake tube from the air box was a little tight but the intake on the motor fit fine. I even used the original 300ex hose clamps, and the stock throttle cable.

[etondaddy]

Originally posted by QuadCobbler
My neighbor gave me his old 400ex carb for FREE :D , he thought it was bad. The lid was bent on one side letting it suck air through the top. After I straightened it out, it works fine. I didn’t have to modify any thing to make it fit. The intake tube from the air box was a little tight but the intake on the motor fit fine. I even used the original 300ex hose clamps, and the stock throttle cable.
Good luck with that...lol that's the way we raced ours for a while....then the air duct came off and it ran like sh@t and sucked a bunch of dirt. Then the intake boot cracked....????? it may have not been from that....but....... it went on just a hair tight. It all fits great now.



Mike Kozura

[dork]

if you can find them, a 350x airboot fits the 400ex inlet and 300ex airbox. the best setup imo is the 400ex airboot. its much larger volume and really works good w/bigger cc's. you just have to take off the snorkel boots and make a bracket for the airbox mount in the rear so the airbox can slide up since the 400 boot is shorter. then you can also run a 400ex filter which flows better. not the most waterproof though.

[macattack]

Bringing this up again…

What are your opinions now, have they changed? What is the best stock setup (not cutting, boiling, etc)?

Carburetor: 400ex
Carb. insulator - Engine side boot:
Air box side boot:
Jets:
Air box:

[dork]

run the stock 300ex carb boot, it fits 400ex and fcr carbs fine. cheapest air boot (airbox to carb) will be using the stock one, stretched to fit. however it restricts modified engines and is a pain to install. i still like the 400ex boot in the stock 300ex air box. you cut the center of the box out to fit the 400ex boot, then run the 400ex filter. this is the best flowing by far, will support 500cc +. or a 350x airboot, but they're hard to find and usually hardened from age which makes them hard to fit and shrink.

[macattack]

WOW!

Great info. just what I needed, thanks!

[dork]

i also trim the seat base where it fits around the air boot, as it squishes the 400 boot a bit. a little trimming takes care of that.

[m0t0xk1d]

we run a 37mm fcr from an rmz dirtbike that we bought off a guy here and it works great. for sure gained a few horse power on the dyno. we have a custom intake on the from we made and we still use the stock airbox boot and its tight but fits.


someone that we know used to run a 35mm fcr from sparks and switched to a 39mm fcr and gained 4 horsepower alone. its a full race motor so that may be a little big for your basic mods

[dork]

do you remember the dyno numbers?

[m0t0xk1d]

with my 37 fcr i have 35 hp and the one with the 39 fcr had 37 hp on the dyno

[stevestauff]

were you running a big bore or modified 300?

[m0t0xk1d]

its a full national engine and its bored to 300cc.

[250rbadboy]

you guys with full race motors like m0t0xk1d
do you run drilled out cdi boxes to get rid of rev limit?

[etondaddy]

Originally posted by 250rbadboy
you guys with full race motors like m0t0xk1d
do you run drilled out cdi boxes to get rid of rev limit?
Yes


Mike Kozura

[m0t0xk1d]

no, we run big gun rev boxes that rev up to 10,500. at about 10,000 the 300s drop of and start loosing power so no need to go more then that.