carb help 400ex

[OregonEXrider]

What I have is a 400ex. The things I have done: Removed spark arrestor/stock baffle thing at end of exaust hole, removed airbox lid, I pulled the main jet jet and it was a 148. I picked up a158 and put it in. Ran it for a few trips. Great power difference, it really noticeable. I pulled the plug and it had a light grey color to it. But I started to notice the exaust started popping like a backfire on de-acceleration.......

I bought a white bros air filter and a 162 main jet. I figured if it was to rich that a 160 would be about perfect. With the 162 if I push the throttle down super fast right off throttle the quad dies. If I push down slowly or just semi fast it doesnt die. I did a search and it sounds like maybe I need to adjust some sort of needle in the carb or buy a different pilot jet or something?

Anyway if you guys could let me know what you think, and also how I get to the needle clip and the pilot I would appreciate it.
thanks
shawn

PS
I ride the dunes and am right at sea leval if that makes a difference.

[cals400ex]

put in a 152-155 Keihin mainjet. for easier starting, you can try to add a larger pilot jet. i would suggest a 40 or 42. the larger pilot jet should help prevent the backfiring. if you don't want to mess with that, just turn the fuel screw on the bottom of the carb counterclockwise 3 turns out from lightly seated.