Weird jetting question

[jt633]

Hi guys I have a 2004 ec250 with an rb head rb carb and ported cylinder. The bike is jetted almost perfect nice and clean not rich not lean no spooge at the silencer the bike has a weird flat spot in the end of the bottom mid range it's always when I'm on the track needing to be on the pipe in 2nd shifting to third to make a uphill jump that delay is making me case it and woods riding the bike will not pull 2nd gear at slow speed unless you pin it and clutch it a bunch. Any suggestions would be great I moved the needle down one notch and it made the bike run even cleaner no difference or correction of the problem. I remember my other gg bikes pulling 2nd gear no problem