Gilera 125 DNA Jet Size?

I have a Gilera 125 DNA bike and have fitted a scorpion style large bore exhaust & sports air filter.

The bike starts & idles OK but dies as soon as you twist the throttle round.

It has the standard needle & size 108 jet fitted in the carb.

Can anyone whom has had a similar problem suggest a starting point for re-jetting etc in order to get the bike on the road again?