dna 125 Gilera?

Hi,
I have a Gilera DNA 125. It is completly standard except pipe. The pipe is a Scorpion. It is a 53 plate 9000miles from new.
When I start it it ticks over nicely but when you put any gas on the throttle it sort of bog downs and dies. When its warmer its better and you can pull away higher revs it goes like stink but its just lower down.
To sumerise ticks over lovely, High revs Brilliant low revs esp when cold a bit rubbish!
Any advice would be lovely and thanks to all