Cold Weather Jetting

I have an 02 400 SX that ran great in the summer time. She would start 3rd or 4th kick. Now, in wisconsin (~1000ft), it is in the teens for temperature and she isnt running well. So I raised the needle one clip and she didnt start. So then I turned the fuel screw mixture in one turn. Still no start. I went back to the intermediate needle setting (#4 w/3 above and 3 below) and turned the fuel mixture screw back to where it was. She started but very rough and ran like crap. Turned the fuel mixture screw out one more time and she starts a bit easier but still runs like crap and doesnt idle. AHHHHH! I am ripping out my hair. Valves are fine, carb is clean. ANyone have any settings for me to try out??? I need to get out and ride on the ice.

Thanks so much guys.

Pull you're Carb part and Clean it out with Carb spray then blow it out with some compress air look though all you're jets before you put the carb back together to make sure you gotten all the dirt out of them.

On a 2 stroke jetting is a big deal when it get real cold 4 stroke are more forgiving but riching the main up by 1 will help the bike out on the top end the air is more thicker it will run richer on air but leaner on fuel in the higher RPM range.

As for the Pilot jet you should be fine just adjust you'r fuel screw out and you mite have to raise the needle up but you should be good.

Also change you're gas out in the tank with fresh gas.

You'e going to want to bump the main at least one size bigger. My 450 was a bit rich over the summer, so I left it. We were out riding last weekend and it worked perfectly.

It was a bit tough to start first time out, but I contributed that to the gas being a couple months old. In WI, they change the formulations around 16 times a year, so it's best to have the freshest stuff, especially when your trying to fire it up in the cold.

Thanks guys,

I will pull the carb and clean it tonight. Now with the fuel mixture screw, if I were to turn it all the way in, do you know approx how many turns I should go out? Or vice versa starting all the way out and then going in?

What would be the cause of my bike not idling though??? No matter how much i turned my idle adjustment it would not idle. Does that relate to the fuel mixutre screw too or needle? My brother brought his 525 EXC up and his bike runs decent but wont idle now either.

I forgot to add, that I did have the needle up one position and it started second kick in the shop. Once I got it in the cold, nothing!

I appreciate the advice and look forward to not having a bruised foot from kicking the bike over and over and over and over (repeat 52 more times)

Cold air = more dense = more air in. So assuming your bike was jetted well for warm temps, it will now be running lean in the cold, so you need to richen it up.

Here in NC, it never gets really frigid, so with the JD Jet Kit that comes with a red needle (warm temp) and blue needle (cool temp), I generally find it sufficient to swap to the blue needle and raise it one position from where I was with the red needle.

That may not be enough to compensate for really cold temps though. Since your bike won't idle well, I'd say you need to go bigger on the pilot for sure. And if you need to do that, I'd bump the main a few sizes as well at least.

I cleaned the carb, it was clean. I put the needle to middle setting, turned idle and fuel mixture screw all the way in and turned idle out two turns and fuel mixture screw 1.5 and it seems to run better, but it is kinda warm ~30 here. I have a JD needle kit coming and also that trick looking fuel mixture screw extension on the way. Hope that helps. Anyone run this? Any recommendations on this, or just follow the instructions (if there are any)?

Thanks for your help guys

JD combo will be right on for running but not addressing starting. What I have done for cold starts is to drill the choke jet to 1mm. Normally I would not recomend drilling jets but the choke jet is not criticle and more jet area there helps! KTM has increased the choke jet for 2009 from the #80 that all 4 strokes have had since 2000 but I have not seen what the size was

bike runs great. I think I just had to get the fuel mixture screw right. She still takes 5 or 6 kicks with the choke on but once she's on she goes like a bat outta hell on the ice. With that JD combo will I need to change any settings again? ie jets, fuel mixture screw?

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