I know this issue has been covered many times, but this still seems to be an issue for my 400EX. A friend who knows his stuff recommended I change out the jets in the carb to a 52 pilot jet and a 160 main jet for the best performance and cold weather starting. I have a Big Gun pipe and a K&N filter on the quad and until yesterday, had no idea what jets I was running. When I opened the carb up, I found a 38 pilot jet,which I believe is stock and a 165 main jet which the previous owner put in place. I thought that a step from a stock 38 to the recommended 52 was too big of a step so I instead opted for a 45 pilot jet and left the 165 main in place since the upper RPMs were always solid. I put it all back together and it still wouldn't start (approximately 28 degrees). I would appreciate those of you who have been through this ordeal if you could give me a good place to start so I don't have to keep tearing the carb out of the machine and buying a hundred different jets. Thanks for your help.

 

Change your cdi back to stock, the WB won't start in cold weather. That's a common known fact. Check the battery and make sure it's fully charged. A valve adjustment might be in order if you haven't done it yet, the 45 pilot may be ok but I would have went with a 42. Change the cdi first.....

 

everythiong i have read says to put your stock pilot at a 40 or 42.

 

Go with the 42 or the 45 pilot. Also, pump the gas about 4-5 times before you start it. The WB rev box will cause the 400 not to start in cold weather. I sold mine because of the cold starting problem.

 

I run the stock CDI in the winter and then change back to the WB in the summer. I ended up getting it started by spraying some starting fluid into the carb. It ran well after it warmed up. I may just have to carry a can of starting fluid with me when it is cold. I originally wanted the 42, but the local cycle dealer was out or 42 jets, so I settled for the 45. Is the 45 going to be too rich in the summer?

 

Are you running with out the airbox lid? you should be! with a 165 main and 45 pilot!
Here's somthing to try: airbox lid off,42 pilot,155-165 main (not exactly sure what size main jet cuz i don't know what big gun recomends) If the 160 is working good for you then keep it in.
If you have a stock neddle jet put it on the second or last farthest down(richer cuz airbox off).
Im not positive but if it's a dynojet needle it should say DJ and then a number on the needle, if thats the case call dynojet and ask what where the clip should be. www.dynojet.com

 

I have holes cut in the airbox lid.