Screaming T25

Hi, Just changed engines in my t25 1.9 watercooled loads of problems due to different engine numbers and cooling system kept going finally had it running but no real acceleration with carb from new engine so put my old carb on drives better but revs high all the time even after a drive any help with this as i may of got in a mess with the wires. This is the vans very last chance as i can take no more will end up a nervous wreck. Any help would be great.