Hey guys new here to this forum. After a lot of $ and a lot of time trying to determine why my 99 Wr400 wouldn't idle without the choke on I found the problem: accelerator pump diaphragm was cracked. I was leaking a bit of gas out the top of the pump where the rod goes in but never would have thought the accelerator pump would have anything to do with the idle. After 2 carb cleanings, a new coil and countless other things I tried I put a new one in and it fired right up and idled great. Hope this helps.