Jetting for a 400ex [Archive]

Pont400ex

10-08-2008, 08:35 PM

I posted this in the tech section also, But i thought i might get more replies here. I need to know the size of the jets to jet my bike correctly. The specs on the bike are 408 kit with highcompression piston, stage 1 hot cam, full yoshi exhaust, aluminum airbox, w no cover wit a k&n air filter. I want to know what size main and pilot to use. Thanks

10-08-2008, 08:43 PM

read my reply in the other thread ...do as it says... and be patient

Pont400ex

10-09-2008, 01:13 PM

im going to pull the jets out today and check them to see what size they are then go from there

Pont400ex

10-09-2008, 05:24 PM

I pulled the jet and pilot out today. The pilot was stock and the main was a 150. I went and got a new pilot, A 40, i was looking for a 42 but they didnt have so it so i went with the 40. For the main i went with a 160. I put all of it back in hooked the carb to the motor. Started it up and it idles wikid high. Can anyone tell me what to look at or whats wrong. Do i need to adjust the air screw or anything? Thanks

10-09-2008, 05:35 PM

go to http://www.jetsrus.com/ and read the faq...this will help you understand jetting...and why just buying one main jet or just wildly changing jetting may not be the right thing...seriously brother, do it...you need to...

Pont400ex

10-09-2008, 06:04 PM

Speedy quad man help me out, Where would you start? Right now i have a 40 pilot and a 160 main. I wanted a 42 Pilot but 40 was the closest. I just threw the 40because there was no 42 and 160 because thats what i was told on another forum. Through some suggestions out. Please. Thanks

10-10-2008, 03:30 AM

i can't tell you the exact jet...it is a trial and error thing...no 2 motors are alike...
first of all, you need to understand how carbs and jetting work...and what jets control what...
pilot jet controls from 0 to roughly 25-30% throttle.
the needle controls about 20% to 80% throttle
the main controls around 75 to 100% throttle
buy a range of jets, run it, do plug chops, it is a trial and error process....

10-10-2008, 03:38 AM

you can also adjust your idle and the air/fuel mixture. the idle is the big knob with the flat blade screwdriver slot. the a/f srew is on the bottom of the carb...
how is the bike acting at full throttle with the 150 main

Pont400ex

10-10-2008, 05:01 PM

After messing with the idle and air fuel mixture screw it idles normal and runs well now, It ran good with the 150 main until it warmed up, then it idled high and the head pipe started to glow. Had a little poping sound, not a full throttle tho, when you revved it at a stand still. But now it runs good andthe head pipe dosent glow, so im in the right direction.

10-10-2008, 07:18 PM

just so you know, you can't judge jetting while sitting in neutral(except for idle only)...the motor needs a load on it...

it was lean with the glowing header...i might even go up to a 170 and start dialing it back

Pont400ex

10-10-2008, 08:11 PM

Yeah i know, it was riddin for some time to see if the head pipe would start to glow and it didnt. Im gonna run it again hopefully sometime this weekend just to make sure its alright.

Wheelie

10-10-2008, 08:18 PM

Lower the clip on the needle one notch from stock, a 42 pilot and a 162-165 main should be pretty close.