Another 440 question

[Meso]

Installed a Athena 434 Big Bore kit on my 2004 LTZ400. Now i'm ready for a YFZ450 39mm carb. My question is, do I need to install all new YFZ front and back boots and Pro Flow snorkle with the YFZ450 K&N filter to complete this part of the mod?

[zeus54]

use a 400ex air boot from the air box to the carb from a 1999ex, eddie sanders racing sells the boot adapter for the carb to mount to the cylinder assembly. get a yfz450 throttle cable and a 400 ex throttle assembly, i use a yfz throttle assembly but people complain about it not being comfortable it works for me fine. i purchased a 41fcr from eddie and the cable is real tight when it crosses over the frame brace (it won't go under the brace because of the adapter that they use ) so check out his 39 kit if you haven't bought one already and get a couple of different sized jets to play with. the pro flow kit is awesome and i recomend you use a foam filter unless you ride the dunes and sand

[ltz400rider118]

hey zeus, does the thumb throttle work harder with the bigger carb or is it about the same? I am looking to put a bigger carb on mine also. and also does the yfz carb require and mods to make it fit?

[zeus54]

i haven't used a smaller carb other than stock it feels about the same, i had a yfz 450 and the throttle felt similar but when i wood peg the throttle it would die and after hours of jet changes and needle adjustments it was still the same so i spoke with a few people that had the expert advice they said it is a matter of rolling the throttle versus pegging it. when it was all said and done they were right i could roll on the throttle but when i pegged it would die. i chose the 41 because it eliminated this problem with a few quick adjustments of the accel. pump and using eddie sanders needle kit. it doesnt matter if i peg it or roll on the throttle it works .post a subject about carb mods making it fit i haven't had to do much other than bolt it up i was not excited when i first started looking into doing all the different mods but it was good with the right equipment and it the carb costed me 512.00 shipped which isn't cheap but i'm glad i decided on it

[Meso]

Thanks Zeus for the feed back. You make mention that you have a 41mm carb. Is that too much CFM of air going in. Perhaps we should go with the 41 as well. We were looking at a 40mm honda carb but thought that was too much CFM. We don't have the cams yet...

[zeus54]

i'm riding between 500-1000 feet above sea level in my area's and i run 170 main with 38 pilot in winter don't know what i'll run in summertime yet but it does great by feel i haven't run on dyno guys from precision motorsports here locally has a mobile dyno and we will find out and i'll post the results, as far as choosing which carb i was told 39's are better for motocross because of the cfm but i'm no expert but i don't think it would matter once you get it dialed in, i'd say that it gets tricky jetting a carb when you run just pump gas instead of (race fuel) check out eddie sanders racing website they have some pictures

[zeus54]

cams are the heart of the system!!! got to be able to move all that air into the motor and get it out, if your still choosing a cam i would check out yoshi's if you can get just their cams they use a longer duration (how long valve stays open) in the intake i believe don't get me wrong hotcams are good but i have seen better from web and curtis sparks

[Meso]

Thanks Zeus, your right the cams are the heart of the engine. Money, money, money. We will get a large tax return this year. Should be mailed off in the next week or so. Then, we will get the cams. Let me know what you come up with. After all is assembled it will be re-dyno'ed.