Misfire 2003 300 ec

[Houghton]

Hi everyone,
I'm new to the forum and just getting back into biking after a 10 year break. I have just bought a 2003 300 ec. The bike has an annoying misfire in the mid range that it struggles to pull through. I have changed the plug, re packed the can and the power valve looks to be operating correctly. I ran it onto reserve the other day and when I re started it, it seemed to run great for about 15-20 seconds then the misfire returned. The carb has a 172 main, 40 pilot, N1EF needle on the second highest notch and the air screw is 3/4 of a turn out. It starts and idles no problem but always seems smokey even when warm (i'm mixing 40-1). current temp is 46f and altitude is around 1500 ft. I'm thinking maybe a N1EG needle would be a good starting point? Any advice greatly appriciated!
Thanks and great forum by the way.