still not sure?

[killer400ex]

this is my last summer here before i ship out for boot and i am planning to do alot of racing and general riding these last few months before i leave. i have been wanting to do a 450r carb swap for my 426 (mods are in sig) for a long time now but i just have not had the time or money to do it, now that i do i plan on trying to get it done before the season starts, im just wondering which year/size carb i am looking for and which holes i have to plug off, ive read tons of threads over the years about people dooing this mod but i seem to have forgotten everything i need to know over the winter, any info would help alot because im trying to order things while i still have time and money lol

[kt1148]

There's a good thread on installing an 04-05 450r carb to a 400ex in the "STICKY" section......

[sheweezy]

http://www.exriders.com/vbb/showthread.php?s=&threadid=314423&highlight=400ex+450r+carb

just search 400ex with 450r carb, tons of info

[killer400ex]

yeah ive been looking at those threads again, orrigonally i didnt want to do this uppgrade because i had just dumped alot of money into my 426 motor and a few other uppgrades and i felt that it was running really strong so there was no point in shelling out another 150-200 bucks to get the 450r carb and then buy a jet kit and spend time trying to tune it right by myself, it just wasnt practical at the time since i had it running like a raped ape. but recently it seems like my stock carb has been starting to get alittle touchy and giving me stupid problems, like it will stutter at really low rpms like right above idle or it will stall out when i pull the clutch in after a long straight away and the jetting will be spot on one day running better than ever and the next day it will run slower than a sprinter at the special Olympics. im just trying to get everything squared away so i can have a solid summer of racing and riding without having to try and figure out whats wrong with it after every other ride. im sad to say it but this might be my last summer owning the 400 that has impressed me from day one, i think it might be time to sell and start over fresh with a new 450, instead of dumping money into a quad to try and help it keep up and beat 450s on a track while trying to keep it reliable at the same time is becoming tedious and expensive, but i still love it none the less and allways will

[sheweezy]

Yeah, you can't beat the reliability of the 400ex, but to be able to compete with a 450 takes quite a large pocketbook, or i guess lack there of seeing funds get depleted quite rapidly...but the decision there is basically whether you want to spend a bunch of money at once with a 400 and make it able to compete or spend small somes of money often to maintain a 450....

as for the carb, if you watch ebay you can typically find a good priced 04-05, get zr's adapter and the jet kit from jetsRus and come out at your figure of 150...I have heard nothing but good remarks for this carb and the throttle response..I can't wait to get my frame back to throw my quad together and try mine out...this carb could be the only thing you need to stay competitive with those 450s....

[sheweezy]

you could also look into Wheelie's +3 timing advance flywheel key...it is designed for oversized bores and higher compression to give you just a little more, once you get done as much as you have already those few little gains can be really noticeable...

[tri5ron]

I'm guessing that with your current upgrades in bore, compression, and cam,...
A properly jetted 450r carb, and one of Wheelie's +3 keys will take your bike to a surprising new level.
If you were to do a dyno run before and after, you'll probably be seeing a realistic 3 to 4 hp increase. That's pretty good for $150-$200 bucks!

You might want to also consider installing a larger oil cooler, and possibly a spal fan.

Chances are your starting to run on the warmer side of the "Comfortable limits",
and adding any more ignition timing or hp, is going to add a little more heat too.

It is certainly "Manageable" and "Do-able", but just keep it in your considerations.
I'd suggest getting a Oil Temp gauge from XR's Only now,... and start monitoring where your temps are running with your normal style of riding.
If it's getting much over the 235-240 mark, you'll want to start thinking about improving your cooling capacities.
(250 is the borderline on where the oil is starting to break down).

[sheweezy]

x2

after running dyno's on many small electric motors and engines, i have noticed it is very obvious that cooler running motors will not only have better hp and torque but also have more longevity