cold water flow out of new tap insert?

Having replaced the entire inside of the cold tap and screwed it all back together the cold water turned back on at the same pressure the water flows for two or three seconds and dies away open it a bit further it happens again until the tap is well open and then it stays flowing. have ckecked inside to see if there were any gung but all is perfectly clear and clean nothing is loose in the replacement valve it's a mystery any suggestions?