Jetting help - 04 RM 250

IMO,  that setup looks lean. 
I would start of with and H series needle on that bike. I would expect it to looks something like this. 

NECH in #3 

45/48 pilot 

168/170 main 

This is with the oem power jet.

Air screw at 1.5 to start out. 

See below for the recommendations and some hints.  Be sure to only use genuine Keihin jets, some of the Chinese ones actually look almost identical but can be a size or two off on diameter or have some differences in orifice length.  Also double check to make sure you don't have an air leak, in the reed block gasket or the intake boot, those rubber parts become brittle with age and it's often hard to see small cracks.

I'd replace the jet block gasket before I went any further. Bad jet block gasket is a jetting rabbit hole.

Diggers jetting specs are very standard for RM250's and work well majority of the time. 160 main is lean. 45 Pilot is fine, NECJ needles work okay but try clip 3. I run Motul 800 at 40:1 in my RM250 but the oil is plenty good enough to be used at 50:1 if that's what you like to mix it at.

But as above ensure everything else is tip top, so float assembly and setting, jet block gasket (if its never been changed the current one could be over 20 years old), no air leaks etc etc.

I've found the timing can alter the jetting on my RM250. Stock timing works well, you can advance it but it made mine run slightly leaner.