Try spraying some "quickstart" in the airbox.
My shee wouldn't start (nothing at all). Sprayed some QuickStart, and it started right off.

 

Use a SALAMANDER!!!!!!!!!!!! Wait about 10-15mins and your golden!! All set to go!!

 

I agree with the heater idea it will work. But if it is froze up you must have gotten some water into the fuel system and maybe it is froze in a line or in the carb itself. I would recommend doing the heater thing and put a little gasline antifreeze in the fuel the kind in the red bottle (isopropyl) but remember one of those bottles goes to an entire tank of gas in a car so I would only add maybe 2-4 ounces of it. good luck.

 

I had the same problem with my 2000 EX. Anytime it got below 40 degrees it would not fire. My dealer told me this was common on the EX and the best thing to do would be to buy an aftermarket CDI box like the one White Brothers makes. The White Brothers is a hotter ignition so it has more spark to start in the cold weather. This did fix my problem and also let the engine rev another 1000 rpm's so I also got extra performance.

 

how much does a cbi box cost and what is the white bros web site.

 

same thing happend to me it wouldnt start so i went to the dealer and they gave me a spark, it ran about a week later same thing happend again what happend is they gave me a bad sprak plug,

 

Dont know about the 400EX , But it was -10 this morning , hopped on the 350X had to kick her 7-8 times and she took right off . I wish my lawn tractor would start so I could use the plow to move this snow . Ive heated it and every thing I could think of , It seems the carb is not sucking gas . I can get it to start and run only by continueing to spray starting fluid in the air box ?? Any ideas on this ??

 

Do not use ether! Bad idea. Ether is very hard on an engine. Use a heater to warm it up, that is what I do. Also take the plug out and make sure it is clean.

 

And its not even really that cold in Kentucky or the Carolinas.

 

yeah it's really cold up here in the great white north. last night i heard it got to like -67 with the wind chill! bet that heater would really need to be working overtime to get an ex started here!