Ultraliner 2

Hi i have a 400 v8 in a 85 superliner that has been sitting for a couple of years before i bought it when you start it idles fine but as soon as you accelerate at about half revs it takes off and revs to full revs and wont deaccelerate have to stop it on stopper then it starts idles ok then if you rev it at half revs it takes off to full revs again thoughts please