Fast bowling?

i m a left arm bowler...when i bowl with the new ball i m only able to get outswingers even if i try for inswinger to right hand batsman i wont be able to ..but then when i bowl with an old ball...i m able to shape it in to righties....wat can be the reason ? n how can i bowl inswingers to RHB with the new ball ? my action is abit like sohail tanvir but i m not wrong footed !!!!