2005 400ex new 38mm carb

[ZOOTERBOY]

Does any one know about the new 38mm carb on the 2005 400ex. The 99-2004 had a 35.5mm. Will this new carb bolt right on? This will be a great performance add-on for those of us who have cams and bigger valves.

[Antnee77]

Why are they making the carb bigger if they aren't doing any engine work? Maybe they will after all.:confused:

[ZOOTERBOY]

If you look on the honda website under specs, it says 38mm carb.

[Antnee77]

No no, I believe you, I'm just trying to figure out why the hell they put it on there when they're not supposed to be doing any engine mods. Oh well...

[Giz400ex]

I thought they changed the carb last year?:confused:

[remlapr]

They didn't change it last year, and probably still didn't this year. It's a typo, or at least was last year. Who knows, maybe it is 38mm now and the mistake was that it got listed a year early last year....

[K_Fulk]

Its always been a 38mm. Just depends where you measure them.

my service manual printed in 2002 has them listed as 38mm.

[ewalker302]

Yep, my Honda service manual dated Sept 98' says 38mm also.

:bandit:

[ZOOTERBOY]

Honda needs to learn how to measure a carb then. The neck on mine (the side that actualy hooks to the head) is 35.5mm. This is how you measure carb diameter.

[MIKE400EX]

FWIW, the last three that I've measured (2001, 2000 & 2002) have all been 38mm. That being the size of the ID on the end that faces the cylinder head.

[ZOOTERBOY]

That's odd. I measured mine and it's 35.5mm. I even used a set of brown and sharp I.D. mikes. I have a 2002. I'm sure the O.D. is 38mm. I will take a measurement tonight and try to post a pic.

I think honda just made it sound better, It's kinda like the 300ex. Honda calls it a 300ex yet it's only a 282cc.

I have put several 400ex carbs on 300ex with any mods to the intake boot. A 38mm ID carb would have a OD of 40-41mm.
The 300ex come with a 32mm ID carb with a OD of 35mm. So a 400ex being a 35.5mm ID with a 38mm OD fits perfect.

Besides unless honda did some head work on the 2005 the 38mm ID carb would have no efect on any performance gain. It may decrease performacne on bottom end though.

Bigger carbs don't always mean more Hp or speed, I know that from drag racing cars.

[cals400ex]

i measured mine to be exactly 38mm's too.

[ZOOTERBOY]

This is taken off a 2002 honda spec sheet..

Engine Type
397cc RFVC air-cooled dry-sump single-cylinder four-stroke



Bore and Stroke
85.0mm x 70.0mm



Carburetion
35.5mm piston-valve with accelerator pump



Ignition
Solid-state CD with electronic advance



Starter
Electric

I'm just stating Honda states what ever they want.

[torqen2k1]

I have a 2004 426ex and the stock carb I am useing has a 38mm carb and yes i double check my measerments. My friend also has a 04 400ex and we measered his carb and it was too a 38mm carb.

[cals400ex]

i checked on this again after reading this thread a few days ago. i can assure you the inside diameter of the carb (where it goes into the head) is 38mm. however, after looking down the carb, there may be some small restrictions that make the carb less than a true 38mm diameter. when you raised the slide up and look thru the carb with a light on the other side it appears to have something in there. maybe it is a 35.5 at the smallest place. this was a 00 carb.

[Rico]

A carb is only as big as it's smallest area within the inside of the carb. SO if the oustide measured 2 foot, the 35.5 inside is what really matters...

I"m beginning to think the carb has been the same from 99 to 05 but the measurements were taken at different areas on the carb by the engineers and then forwarded to marketing for print.

[Steve-o 400EX]

Originally posted by Rico
A carb is only as big as it's smallest area within the inside of the carb. SO if the oustide measured 2 foot, the 35.5 inside is what really matters...

I"m beginning to think the carb has been the same from 99 to 05 but the measurements were taken at different areas on the carb by the engineers and then forwarded to marketing for print.

exactly right. U need to measure form the smallest point, that is why u can get it bored to a 38mm.

[torqen2k1]

Yes I have a 2004 400EX and measured the inside diameter the part that hooks up to the intake manifold and it was 38MM. Yes I now how too measure.

[dndj]

The honda part number for the carb has not changed from 99 through 04: 16100-HN1-013

I don't think the carb has ever changed. This is from a 2000 EX.

Hey Zooterboy, if you're still measuring 35.5mm at this spot, please post a picture.

http://www.aracnet.com/~dndj/DSC02248.jpg

[cals400ex]

yes, where the carb attaches to the intake boot is 38 mm. however, open the throttle up and look inside the carb. you will see some "restrictions" in there that would actually make the carb smaller than 38 mm. make sure you have light shining thru the carb or it may be hard to see. also, the throttle has to be opened to see it.

[dndj]

Originally posted by cals400ex
yes, where the carb attaches to the intake boot is 38 mm. however, open the throttle up and look inside the carb. you will see some "restrictions" in there that would actually make the carb smaller than 38 mm. make sure you have light shining thru the carb or it may be hard to see. also, the throttle has to be opened to see it.
Totally agree.

Zooterboy said earlier that he made this same measurement and it was 35.5mm. That's why I posted the pic for clarification.

[Rico]

Originally posted by cals400ex
yes, where the carb attaches to the intake boot is 38 mm. however, open the throttle up and look inside the carb. you will see some "restrictions" in there that would actually make the carb smaller than 38 mm. make sure you have light shining thru the carb or it may be hard to see. also, the throttle has to be opened to see it.

I guess when I said "inside" the carb that really meant the outside of the carb to some....:huh

Mines a 38 but only because it was honed out by sparks racing. :blah:


Cals your exactly right on your statement. The inside of the carb tapers in which makes the inside smaller than the outside, which is what we've been saying all this time. Maybe our wording is coming up in japanese or something on some pc's....:confused:

[dndj]

Originally posted by Rico
Maybe our wording is coming up in japanese or something on some pc's....:confused:

Why the attitude? :confused: It seems as if you took the post I made with the 38mm measurement picture wrong. I fully understand your point that the internal bore diameter is what matters, and on the EX carb it's something smaller than 38mm.

I only posted the pic as information regarding the 35.5 vs. 38 question which originally started the thread.

"Does any one know about the new 38mm carb on the 2005 400ex. The 99-2004 had a 35.5mm. Will this new carb bolt right on? This will be a great performance add-on for those of us who have cams and bigger valves.:

I have learned a LOT through this discussion and everyone's input. I too had some confusion from the two different numbers floating around out there on Honda spec sheets. Here's what I concluded:

1. Honda published 35.5mm on marketing spec sheets from 99 to 03, but changed the number to 38mm in 04

2. Honda factory service manuals say 38mm for all years

3. Honda carb part number has not changed from 99 to 04

4. Carb measures 38mm at opening closest to head but something smaller than that internally inside the bore. This smaller diameter is the limiter.

Thanks to all who contributed to this thread! Appreciate your input and insight. Might want to look into getting my carb bored out as well... ;)

[Rico]

Originally posted by dndj
Why the attitude?


Sorry I hadn't had my morning beer yet.....:o

:D


Also.... Rocky Ridge Racing is the cheapest place I know of that does carb boring. $125 i believe.

[cals400ex]

so, has anyone looked down their 04-05 to see if it tapers too?? i just wanted to clarify this so when this topic comes up again we can refer everyone here. i am betting your philosophy is correct rico, where the measurements were taken from different spots.

[sickmojave]

Originally posted by cals400ex
so, has anyone looked down their 04-05 to see if it tapers too?? i just wanted to clarify this so when this topic comes up again we can refer everyone here. i am betting your philosophy is correct rico, where the measurements were taken from different spots.

I agree I would love to see this settled once and for all. :o

[K_Fulk]

Originally posted by sickmojave
I agree I would love to see this settled once and for all. :o

Word... This should go in the faq section and when this comes up next we can just link them to this. Till it sinks in for everybody.