my chainsaw won't accelerate from idle speed?

I have a spear & Jackson chainsaw 2.5 years old, it was running ok, then when I tried to use it again it would not start did all the usual checks, plug air filter and new petrol mix, managed to get it going today, but now it will not accelerate when I squeeze the throttle, any ideas as to what the problem could be now, the saw is a SPJCS 3740 spear & Jackson serial no A R G - 6227