rabbittingman

Hi everybody,I am the owner of a sr250 1985,for about 2 months now and I was wondering if someone could give me some advise on it. when I stop at a trafficlight the bike really races like mad and then very very slowly it slows down to idling speed,I sprayed easy start around the manifold and there is no leak there,the trottlecable is not jamming either,something to do with the carby itself,anybody any suggestions please? tia