trouble starting in cold weather

[jesseweaver]

My EX wont start now that its starting to get colder. it started fine all summer, but i guess its the pilot jet? im not too fimilar with jetting, ive never even had the carb off the quad. i know when i bought it the guy said it had a jet kit in it. So, do i have to change the pilot jet, and will i have to buy anything? would it be easier to do this myself, or should i take it to a shop?

[300exOH]

All you need is a 42 pilot and a few minor hand tools. It's very easy..

Here's a "how to" from the "articles" section (Just below the atvriders logo at the top of every page) You'll find some other goodies in there as well.

http://www.atvriders.com/articles/pilotjet.html

[jesseweaver]

OK thanks, that helps a lot. Where is the best place to get a new pilot jet? how can i tell what jet is in it right now?

[300exOH]

Originally posted by jesseweaver
OK thanks, that helps a lot. Where is the best place to get a new pilot jet? how can i tell what jet is in it right now?

It should have a 38 pilot if it is stock. You will need a 42 keihen pilot (not sure what series). You MIGHT be able to get one at your local dealership but you might have better luck calling C&D racing...they should have no problem getting you the right jet. The pilot you have should have numbers on the base that tell what size it is.

[asa400ex]

It might be form your CDI box only if it is an aftermarket one. Aftermarket CDI boxes have a hard time starting in cold weather.

[wizzade]

42 keihen N424-26 series piot jet.

I got mine from www.jetsrus.com

[Ruby Soho]

my 440 starts easy in 5 degree or 90 degree weather.. its never been hard:confused:

[250exkid]

wut size pilot jet should i put in my 400ex if i have a hmf slip on?? and is it ok to mix and match jets brands?

[CarGuy7a]

Originally posted by 250exkid
wut size pilot jet should i put in my 400ex if i have a hmf slip on?? and is it ok to mix and match jets brands?

it'll be fine. i'm running a keihin pilot with dynojet jets. i don't think anyone makes aftermarket pilot jets. the pilot jet only controls your idle to 1/4 throttle mixture.

the size will depend on altitude and mods. where i'm at i can get away with running a #40 pilot with the mods i have with a vented lid and it'll start just fine without the choke in warm weather and it starts fine in cold weather with the choke on.

[jesseweaver]

how can i tell if it has a jet kit in it right now? also, if it helps, i dont have the choke on anymore, so that could be some of the reason.

[BlasterEaten250]

They probably just put a bigger main jet in for the pipe. The main jet should have a number stamped on the side. Stock is 148. When you are starting it for the first time, try pumping the gas once or twice before you try to turn it over, that usually works really good for me. Most of the time I don't even need the choke unless it's like 10* I also have a 42 pilot though.

[250exkid]

umm im at like 800ft abouv im in south east oconomowoc wisconsin so do you no wut size pilot i should jump up to? and yes its a pain in the *** in the warm weather to just to warm up and HORRIBLE in the freezing cold!

[BlasterEaten250]

Originally posted by 250exkid
umm im at like 800ft abouv im in south east oconomowoc wisconsin so do you no wut size pilot i should jump up to? and yes its a pain in the *** in the warm weather to just to warm up and HORRIBLE in the freezing cold! im not to far from you, try a 42 pilot

[250exkid]

ok will do. do you no wut the stock size it?

jesse...

The CDI box comes from an XR250 kick start bike. It's equipped with a circuit
designed to help keep the engine from "kicking back" on the rider.

What it essentially does is not fire the spark plug if the engine doesn't crank
above a certain RPM. This preset RPM level is just barely under the normal
crank speed of a 400EX... So, throw in some thick oil & cold temps, or simply
a low battery, and it's just enough to cause the engine not to start.

To verify that this is your problem you can do two things. You can put the
stock CDI box back on and see if it fires right up (it probably will), or you
can roll start it.

[cbr929rr]

if your valves are out of adjustment that will also hurt cold weather starting, you could also construct a block heater for winter snow riding. I purchased a 2 level heat gun from harbor freight for $10, then I took some scrap wood and drilled a 2" hole near the top of a 6"wide by 24" long board. I put the barrel of the heat gun through half way and glued and screwed a piece of wood on the bottom of the handle so it would stay put. I then measured from the garage floor to the top of the cylinder and bottom of the head and cut the fixture on the bottom to reflect that height. Last I made a base running across the bottom so it stood by itself.
I turn the gun on low go back in the house for 20-30 minutes while the engine heats up I get dressed for riding and go out and fire the engine up. It stays running because it's already pretty warm.
Be careful of the plastics near your cylinder head, not a problem if you constructed the fixture to the right height. And if you have nerf bars you measure from the top of them to the cylinder head. It would probably be about 11" shorter but all depends on tire's and suspension so do your own measurements.
It's not as hard as it sounds, so don't make it complicated it's just a set of hands so you don't have to do such a boring job.