The user manual has a table in it. You can download at
www.gasgasmotos.es
I'm not familiar with the older carb AS series 1, but from what I have read it likes to be jetted much richer than the newer ones. As such disregard a lot of the info re N3EW/NEDW etc that you may read. You can however substitute and try an NEDF/NEDG etc if you want to do some testing of different needles.
The things that stand out reading your current setup is 1) its cold and 2) thats a lean main jet. If you were happy with the response of 38 N1EF#3 but it fell flat up top I'd suggest trying a 175/178 main jet. That would be typical for those conditions/temps/clip position.