250-500cc Hanging idle

My 04 wr250 has some hanging idle issues when I’m rolling in gear say 3rd gear and I pull the clutch in the idle stays high then sort of fluctuates down slowly but goes up and down until it reaches idle and the bike sort of jumps as it fluctuates ever so slightly. Now I played with the mixture screw and idle screw and when I had it idling very low where it would stall without a bit of gas it ran great the issue was resolved. But at that setting it was wayyyy too low where I couldn’t come to a stop without it stalling if I didn’t give it gas right away, like as soon as the clutch was pulled in it wanted to stall so it needed gas. Once adjusted any higher I get the idle issue again. Could this be a jetting issue should I put a larger/smaller pilot jet? I’m pretty new to mechanics on the bike but I’m comfortable with taking a part the carb and jetting it I just don’t know how to tune it correctly. Also my spark plug was black which tells me it’s running a bit rich just wondering if this could be the issue and how I should go about trying to fix it. Thanks in advance!

First thing to do is check the intake system for air leaks, particularly between the carb and the cylinder, cylinder base gasket and flywheel side crank seal.
Then check float height in the carb- refer your owners manual or google for specs and method.
Then and only then look at air screw / pilot jet adjustments.

agree wit Oldscool on checking for leaks first
that said, good quality (flammable) carb cleaner is the easiest way to check, while it's idling spray in front of the cab and if the idle rises find the leak

Thanks a lot guys I’ll bechecking it out today.

Complete opposite for me !!! firstly you fit s new pilot jet of the correct size to see if that cures it as the one in the bike may be festering due to shitty fuel and if that dont fix it do all the above. 10 minutes work and a few bucks (if that) vs hours of toil trying to get to the bottom of the problem .

I bought a few different size pilots gonna try it out tomorrow