39mm FCR Upgrade - Is it Worth it ?

[Langbolt]

Hey Guys....I have a feeling the Stock carb on my 400ex is JUNK

I've rebuilt it with all new components and it still runs WAY too rich for my setup:

Stock cam
11:1 piston 0.040" over
K&N filter - Lid removed
Pro Circuit Full Exhaust
New Valves, Springs & seals
New Dyna CDI

Jetting is:

42 pilot
Air-Screw 2 turns out
Needle - 3rd clip
148 Main

Plug is BLACK DRY SOOT

Starts Great!

Idles Great!

Off Idle is Great!

But Stutters like crazy past 1/2 throttle...bah,,,,bbbb,,bah,,,,bbb,,bah

Ignition is good.....I can hold the plug 3/8" away from the head and it still jumps a spark!!!

Do I really need to go leaner than STCK Jetting to cure this ???

Or Is my Carb just another paper weight ???



:mad:

[AtvKid4Eva]

your running a STOCK main jet in your carb..start with a 165 main and see if it runs better, if not go up. We run a 180 main in my brothers 426 with a full system, runs perfect.

[400exshop]

It's a lot nicer set up so if you can get one cheap get it.

[Langbolt]

Yep....I'm running a Stock JET - 148

I had a 160 in it and the plug came out BLACK and I could see black smoke out the tail pipe

I tried a 140 last night and it was a bit better

I'm thinking it might be the Air Cut-off valve.....So I ordered on today

It's almost as if the needle jet has been hacked (opened up) as it floods out when the throttle is opened past 1/2 throttle

Too much fuel in the carb.....I'm gonna change the JET tonight

The floats are good....or the overflow would be dumping gas

I'm really stumped with this!!!

:mad:

[400exrip]

I run the FCR39mm but I would only suggest it for built race motors, it makes a ton of difference. But it does cost a lot.

Maybe if you want to, you can send your stock carb to someone and get them to bore the stock carb, that will make a lot of difference too. But when you bore the stock carb you have to run Big jets.

[400exshop]

if you have the fcr and dont want to run it let me know i have to stock carb and a swist throttle ill tread you....

[malibuj]

I ran a 04-05 450r carb on mine and it made a very noticable difference. Sold the quad, still have the carb and the adapter sleeve.:D

[hondarider421]

id do the stock 04-05 carb its alot cheaper and same power out put the best thing is its a bigger carb even though its no flat slide

[Colby@C&DRacing]

I would recommend the FCR carb. It is a pricey option but well worth the money.

[400man]

Im using a stock yfz450 carb on mine, its a 39mm fcr. It doest take a little bit of custom fitting to work, but im extremely happy with it. I never have to use the choke to start it, just pump the gas a couple time. and I also have a lightened flywheel and with the FCR carb it sorta feels more like a 450 motor the way it revs quicker and smoother. I forget what jetting im running but it runs damn good for me. heres a few pics of it, kind of a tight squeeze in place of the stock carb.

http://i417.photobucket.com/albums/pp255/ky2stroker/400exfcrcarb003.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400exfcrcarb004.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r009.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r010.jpg
http://i417.photobucket.com/albums/pp255/ky2stroker/400ex450r011.jpg

[atvrider13]

04 and 05 450r carbs are alot better over stock, FCRs are even better than them