Need jetting help bad!

[ghak99]

Here is the quad:
250x, 400ex carb, KnN jets and needle, KnN filter, 350x air boot, No lid on air box, 12:1 piston, Full race web cam, Matching Spring kit, Heavily ported, Sparks X6, Racing fuel. I live in north missouri as far as elevation goes.

Problem:
Has a dead spot when mashing on it from idle to wide open, and pops during deceleration. I have tried all kinds of jet combos and can not figure it out. I have cleaned the carb completely with carb cleaner and air, with no changes. It doesn't matter what jets are in it, the plug reads lean, even though the large jets feel and smoke rich. Some explain the lean reading by using race fuel, but I am not sure about that. I also run the valves and nothing changed.

Any suggestions are greatly appreciated!

[F-16Guy]

Sounds like you're lean on the pilot circuit or needle. Try going up on the pilot jet, down on the main, and maybe moving the needle clip down one groove. Backfiring on deceleration is a good indicator that you're either lean on the pilot circuit or have a leak in your exhaust.