Hi
I run a 2005 250 EC and had similar running issues to you.
- Check Reeds - broken tips / poor sealing
- Stripped cleaned and Adjusted PV
- I then replaced crank seals (optional but not that expensive to do)
- New plug
- Clean filter
- Repacked exhaust and welded up crack in rear pipe
- Replaced NE1F with DDK (clip 3) needle combined with 45 or 42 pilot
Bike has been so much better, clean running, pulls strong - Fuel economy pretty much doubled. (Note I use for mostly green lane runs so lots of low speed technical stuff between high speed road sections)
My advice is to ensure all the basic health checks are made before you play with jetting - if something fundamental is wrong you need to fix that first. When happy the basics are good then as a start the DDK works well
Hope this helps..