Worried that it's running lean

Sorry to bother you but can I ask for a bit of advice
As you know I have been having a few issues with low rev stutter ( as do many KDX 220 owners ).My pilot was 42 having changed to a 38 the stutter got a little better, I went to a 35 the stutter is much better but I'm worried that the bike might be a bit lean now, the air screw makes very little difference now not like when I was running the 42 and it does feel like it's lost a bit of it's snap.
Thanks Jono

2003 KDX220 UK spec stock other than the snorkel removed and running 40-1

Hi Just to add that I have had a look at the plug and it's a nice dry mid brown colour so It might be ok

Hi thanks for that I took it out for a run about an hour ago and it does feel flat when you crack it open I have replaced the pilot to a 38 and it feels more snappy. I'm going to give it another go tonight.
Thanks Jono