2005 400EX Jet questions

[Nate/05 400EX]

I'm currently located in Southern Illinois which is about 600ft above sea level. I have a 2005 400EX with an HMF slip on and a K N air filter with the lid on the air box. I may end up changing to the K N air lid that functions as the pre-filter (is that a good idea?). I have read in some places to go with a 152 main jet and 42 pilot and other places to go with a 155 main jet and 42 pilot. I was wondering which to try out. Also, which brand of jet should I go with? I think my bike may be running too lean right now as it pops on deceleration, doesn't idle well unless it's been warmed up for 10 mins, and it doesn't run at all if you turn the choke on. I appreciate any and all help.

[Mike/HMF]

We recommend starting with a 152 main, and 42 pilot with the air box lid on. This will get you in the ball park, but fine tuning is up to you as every machine is a bit different. Removing the lid or switching to a higher flow lid will require a larger main jet and get you more power. The only downside to doing this is having to service the air filter more often.