yfz 39mm carb on the 400ex?

[ae13291]

hello i know there is many threads about it but search sucks on this site, what all is needed to install the 39mm yfz carb on my 02 400ex? i just got the carb, im currently at a 160 main and 45 pilot should i transfer those right over to the 39mm carb or will it be differant? thanks guys

[mattl31]

subscribed...i would also like to know this. im currently swapping from stock to a 41mm FCR as well.

[honda400ex2003]

anything can be adapted to work. i would say that going up to a 168 would be a good starting point along with the 45 pilot and see how it goes from there.

it will be half way close as long as there are no leaks or anything in it.

steve

[ae13291]

thanks for the replies, other then the carb itself, do i need a new cable? would the gas tank clear the top of the carb? anything else i need to know before i tackle the job? i know alot of people have done this to a 400ex

[mattl31]

you'll need the throttle cable off of a 06'+ 450r. While not necessary, supposedly the 450r fuel line also makes the job easier. It should fit fine, but it will be tight. The only other thing you might need is a billet adapter that will make the carb closer to stock carb dimensions, lengthening it front to back to allow it to mate up to the factor air boot.

I'll be installing mine tomorrow, and will be sure to take several pictures for you.

Heres mine:

http://inlinethumb36.webshots.com/45987/2356776800103197556S600x600Q85.jpg (http://good-times.webshots.com/photo/2356776800103197556QJJxuT)

http://inlinethumb06.webshots.com/45125/2541681810103197556S600x600Q85.jpg (http://good-times.webshots.com/photo/2541681810103197556TbkJBu)

[400man]

heres some pics of mine. its takes a little bit of custom work, but it all works out pretty good. I used a rubber adaptor piece I got from Lowes in the plumbing section. I used black electrical tape to build up the airbox side of the carb for the adaptor boot to fit snug ( it took awhile to even find anything that would work close enough). the intake boot on the motor is a tight squeeze but its easy with a hair dryer to heat the rubber. I just used the yfz throttle cable, works perfect.

http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r011.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r010.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r009.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r008.jpg

[ae13291]

man that thing is in there TIGHT! thanks alot for the pics that will help me a ton, any way you got a part number on that adapter? i will order the yfz cable while im at it, but im gonna have to do something about that bowl screw, it looks as if its touching, thats no good at all.

[mattl31]

Well I got mine on today. Not going to say it was a total pain in the ***, but it definitely wasn't a 30 minute install by any means.

1.) Had to open up the intake boot (that bolts to the head) to get the carb into it (easy deal with a dremel)

2.) Had to open up the intake side also, to get the air tube to fit over the carb adaptor. Also not too big of a deal, but it did take a good amount of rubber removal, along with some severe heat-gunning to get the rubber soft.

3.) Fitment between the gas petcock and the carburetor is VERY tight, as in they're touching. Not sure if this is anything to worry about, however I'll keep and eye on it to make sure there isn't any damage taking place.

4.) With my install, the tank now sits slightly higher, as the carb sits a good bit taller than that stock one. Not a huge issue, but I did have to tweek my side plastic panel mounting points to get the fuel shutoff switch centered in its opening.

Aside from that, fairly straight forward install. I got it running, but its not running well yet. Havent had a chance to mess with any tuning, but with a 170 main, 42 pilot and the F/A screw 2 turns out I cant keep it idling without feeding it gas, it occasionally backfires and seems to be running extremely lean.

This is a 40mm carb, on a 407cc 11:1 Wiseco Piston, Ported and Polished head, Stage II Hotcam K&N filter in a CFM airbox (no lid), FMF powerbomb header and FMF Ti-4 Pipe.

Any reccomendations on jetting? On the stock carb it ran well with a 172 and 38 combo.

[ae13291]

^^^ go with a bigger pilot jet, try a test first, ride it and get up in the rpms and just decelerate if you hear it poppin go up on the pilot jet,

[400man]

oh and I forgot to say that I had to do a little cutting and trimming on the carb itself. I was having problems with the fuel petcock nipple (:rolleyes: ) hitting the plate that coves the TPS thing with the plug-in, after some cutting and grinding I got it to fit perfect and it looks like it was made just for it. I'll get some pics of what im talking about later.

[sneaky11]

hey guys! I'm in the same process with the 450er FCR... put that on the bike and I cant get this thing running without the choke on... At the moment I push choke off, it dies...

When I first got the carb, it had a 120 main :confused: 42 pilot...
I'm really confuse... you guys runnin like 170!! Someone can explain me why I need more fuel then a 450r stock??

[ae13291]

Originally posted by 400man
oh and I forgot to say that I had to do a little cutting and trimming on the carb itself. I was having problems with the fuel petcock nipple (:rolleyes: ) hitting the plate that coves the TPS thing with the plug-in, after some cutting and grinding I got it to fit perfect and it looks like it was made just for it. I'll get some pics of what im talking about later.


as long as it works right? im thinking about machining a piece of aluminum to work as an adapter but i gotta throw on that carb and take some measurements, or i can just go and find something at lowes.

[mattl31]

well i got mine closer, but i still dont think its perfect.

I ended up at a 50 Pilot and a 175 Main, fuel screw around 2 turns out.

Only thing that seems out of the ordinary is a slight chop at idle (think cammed big block lol), and it doesnt return to idle very quickly with the blip of the throttle.

what do you guys think?

[honda400ex2003]

you could try to tune the f/a the same way that you do on the 400 carb or the 450 carb.

http://s759.photobucket.com/albums/xx239/rocky_mtn_honda/TRX400EX%20Manual%20Pages/?action=view&current=carbadjustment.jpg

that will get your pilot circuit about as good as you can get without a sniffer to doing it.

Is it hanging after a blip of the throttle? that would indicate a lean condition in most cases or an air leak somewhere causing it to hang. most of the time it is a leak though.

how does the plug look at that jetting?

steve

[mattl31]

Originally posted by honda400ex2003
you could try to tune the f/a the same way that you do on the 400 carb or the 450 carb.

http://s759.photobucket.com/albums/xx239/rocky_mtn_honda/TRX400EX%20Manual%20Pages/?action=view&current=carbadjustment.jpg

that will get your pilot circuit about as good as you can get without a sniffer to doing it.

Is it hanging after a blip of the throttle? that would indicate a lean condition in most cases or an air leak somewhere causing it to hang. most of the time it is a leak though.

how does the plug look at that jetting?

steve

yeah it just doesn't return to idle quite like it should. it does, just not nearly as fast as the stock carb. im sure a lot of that can be contributed to the fact that this 40mm flows so much better than the stocker, however im still going to try to get it perfect.

the plug has several hours on it, but it remaining a warm chocolate color. I cleaned it well and will be keeping an eye on it.

that procedure seems pretty effective...just wish i had a tach to get a hold of :ermm:

[honda400ex2003]

you can get it pretty close just by listening to it. just let it sit for a few seconds inbetween adjustments and hit the throttle once in a while to sort of reset it.

i hope that helps out a bit, no matter what pilot is in it you should be able to get it pretty close between 1-3 turns out on the f/a steve

[400man]

a couple more pics

http://i417.photobucket.com/albums/pp255/ky2stroker/400exfcrcarb003.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400exfcrcarb004.jpg

[honda400ex2003]

it looks like it fits in there pretty nice. im not sure about the plastic connector and would def verify that theres no leaks in it but looks like it will work if it is sealed up.

i like the pull choke, it is in a good place to use also. steve

[mattl31]

Messed with it just a bit more, seems better. However now, when I start it with the choke on it fires right up but idles way faster than it should. As soon as I pop the choke off though, it idles where it should. Normal?

[honda400ex2003]

mine does the same thing, i would say it is pretty normal. just about everything i have with a choke idles high with it on, that is the effect of the choke really. it is supposed to raise the rpms to keep it running better.

glad to hear you got it running better!

what was your final setup?

steve

[mattl31]

50 Pilot 175 Main NKYT Needle 3rd clip from the top, A/F screw 1.5 turns out.

Need to ride it now!

[ae13291]

i had a problem with the hanging idle on my yfz, make sure you adjust the fuel screw until the engine seems to be running most efficient (the highest rpms that you can get it by adjusting the fuel screw) once the rpms are high enough, adjust the idle screw down until it reaches a normal and stable rpm.

[mattl31]

i think i found the culprit...

somehow im getting fuel leaking out of the main carb body and into the throttle spring area....a massive amount. i'd imagine wherever its leaking out, air is also leaking in and causing the floating idle. not sure if there is any sort of seal on the throttle shaft, or if maybe the slide plate is worn. i'll investigate tomorrow and report back.

[mattl31]

Update:

I'm an idiot

Slide plate was in upside down! Runs like a dream now.

That is all!

[honda400ex2003]

congrats on getting it running good. steve

[mattl31]

Originally posted by honda400ex2003
congrats on getting it running good. steve

thanks steve, you're always a great help

[ae13291]

ok so ordered a bunch of oem parts, i need to remove the old carb so i can get some sizes and im thinking about making a adaptor on the lathe.

[SHIFTx450]

So how well does this perform as a performance mod? What's it feel like when riding? Power? Throttle response? Compared to a 450? I am ordering a stock 40mm fcr crf450 carb for my hybrid, and am gonna put the existing YZF426 39mm fcr on my 400ex. Just wanna know what to expect.

[ae13291]

im still doin mine just being lazy but it should be a huge upgrade, a stock 400ex is really lacking a bigger carb

[400man]

Originally posted by SHIFTx450
So how well does this perform as a performance mod? What's it feel like when riding? Power? Throttle response? Compared to a 450? I am ordering a stock 40mm fcr crf450 carb for my hybrid, and am gonna put the existing YZF426 39mm fcr on my 400ex. Just wanna know what to expect.

one of the main things I noticed was how much easier the thumb throttle feels. I used the stock yfz throttle cable and the spring tension is probably half compared to the stock 400ex carb. also it revs up alot faster (when jetted correctly). mines not perfect but it still revs up alot faster compared to the stock carb. mines basically a stock motor, but when ever I start upgrading to bigger bore and more compression/bigger cam the fcr carb should shine even more than it is now.

[ae13291]

ok guys tell me if this will work. i was thinking of using a machined pipe to put on the front of the carb, toward the cylinder head side in order to push the carb more back to fit into the intake boot. i was thinking this would be great and it would be a better fit because the starter wont be close to it but i was thinking that pushing the carb towards the back of the quad may cause a bog in the throttle, if i crack open the throttle the fuel wont reach the cylinder in time? what do you guys think. please let me know im about ready to put this damm thing in already.

[CJM]

Id say its a good idea, but cant know for sure what problems may arise since Ive never done it before.

I recall someone else who used one of these carbs got a piece of rubber plumbing adapters and used that to connect it to the head/boot.

[0101]

Originally posted by CJM

I recall someone else who used one of these carbs got a piece of rubber plumbing adapters and used that to connect it to the head/boot.

As seen in post 6(?) on the first page, except it didn't push the carb back... it just helped the tube connect to the airbox.

[400man]

Originally posted by 0101
As seen in post 6(?) on the first page, except it didn't push the carb back... it just helped the tube connect to the airbox.

if you did space the carb back from the head and closer to the airbox, you would still have a problem with the airbox boot cause it still wont clamp tight on the yfz carb cause its smaller than the stock400ex carb.

[CJM]

Could cut some tubing and use it as a spacer, I still think its all up to the user in the end to make it fit 100% way they want.

[SHIFTx450]

Originally posted by 400man
if you did space the carb back from the head and closer to the airbox, you would still have a problem with the airbox boot cause it still wont clamp tight on the yfz carb cause its smaller than the stock400ex carb.

Mine fit like a glove ;)

fernco between head and carb, everything else fit and fell into place like it was meant to be there.

Just additional input, I am extremely satisfied with this mod. My Wife's 400ex now feels like a totally different animal. I recommend this as a must have mod for any serious 400ex owner.

[ae13291]

Originally posted by SHIFTx450
Mine fit like a glove ;)

fernco between head and carb, everything else fit and fell into place like it was meant to be there.

Just additional input, I am extremely satisfied with this mod. My Wife's 400ex now feels like a totally different animal. I recommend this as a must have mod for any serious 400ex owner.

please if there is any way you can get some pics up i would realllllyyy appreciate it. so i take it that the quad has been running fine? im still a little skeptical about pushing the carb back, the heat and more time it takes for the fuel to reach the cylinder may result in evaporated fuel and hesitation, but if you are running it this way and had no problems i may consider this.

[CJM]

Originally posted by ae13291
please if there is any way you can get some pics up i would realllllyyy appreciate it. and what exactly is a Fernco?


Originally posted by CJM
rubber plumbing adapters

You can buy them at home depot. Its a rubber adapter found in the plumbing section.

[ae13291]

Originally posted by CJM
You can buy them at home depot. Its a rubber adapter found in the plumbing section.

yea i googled that right after i asked, damm that was a fast post.

[CJM]

Originally posted by ae13291
yea i googled that right after i asked, damm that was a fast post.

Yea. its liek 2 bucks I have a few laying about for other stuff-works really good to seal stuff up.

[ae13291]

^^ is there a company i can call that i can ask them a question like if its ok to move the carb back from the original location? will sparks racing or a car company know? im thinking it will be a power lose moving it away from the motor.

[CJM]

Originally posted by ae13291
^^ is there a company i can call that i can ask them a question like if its ok to move the carb back from the original location? will sparks racing or a car company know? im thinking it will be a power lose moving it away from the motor.

You could try calling sparks, but I have never had good luck with them. They wont even release thier cam grind (which imho speaks to me like its someone elses cam they are just rebadging lol).

I honestly do not think moving it alot would effect it to much-how much moving are you talking about-1/4" or less should be fine.

[ae13291]

tomorrow the stock carb is coming off after i get off class, that thing is leaking from around the accelerator pump from last ride, so it leaves me no choice but to replace it now rather then spend money on a new gasket. if its only a 1/4 or even 1/2 that would be no problem i think it would be safe to move the carb back. i will try calling sparks, hopefully somebody will be kind enough to share there knowledge.

[400man]

I know on a two stroke with a reed spacer it affects the powerband, forgot which way its for more topend or more lowend, depending on which side of the reed valve you put the spacer on.

[ae13291]

decided to just mount it in stock location. it actually fit great, im goin to have the spacer made tomarrow and this sucker should drop in place. im installing a thumb style air/fuel screw hopefully i can adjust it considering its pretty close to the starter. current jets in my 400ex is 45 pilot and a 162 main or 165 not sure on that. should i transfer those straight over to the yfz carb? or will it be differant?

[SHIFTx450]

I have a 48 pilot, 165 main, needle 3rd clip down, don't know where the air screw is, I just adjusted it to where it was good.. Boyeson quickshot 2, 55 leak, and the jetting is absolutely perfect on mine.

I apologize I haven't gotten out to get a pic just yet, but it seams you're good. Hey good luck.

There's absolutely no difference that I noticed in having the carb directly against the head vs. spaced out with a fernco. I had it directly mounted to the head just to even see if it would start and check the jetting and stuff, she fired right up,than I remounted with the fernco spacing the carb back away. It also helps it to clear the gas tank in this location. Bike still fired right up, absolutely no difference in anything. F'n rips man. Strongest running 400 i've ever ridden..

[SHIFTx450]

Gimme some time, I'll help you out and get a pic up later on today. I gotta go change out my rear shock today, I'll take it then.

[ae13291]

oh thanks man, if you could get pics that would be great. what was the exact jetting you had in your 400 before you went to the new carb? also elevation and what mods are done to yours?

[SHIFTx450]

I am not sure of the specs as I've never had it open. I do know that the motor was supposedly a built 416, but was a turd when I bought it. I was a real POS. Paid 900 bucks for it so you get the idea of how bad a shape it was in.

It's since had a complete overhaul as far as suspension and controls go, exhaust and intake stuff. The motor is still how it came with the exception of me replacing silicone with gaskets :rolleyes:

Needless to say it was never jetted right because this FCR woke this thing up night vs day.

Here's some pics:

[SHIFTx450]

wtf it says file size is too big... what is your email address? I'll email you them

[ae13291]

pm sent

[SHIFTx450]

Pics sent, check email Mo

[ae13291]

thanks again for the pics bro, im going to post them up in the thread so it can help anybody else looking to do this mod. im going to take a bunch of pics tomarrow of my set up and i will post them all up.