gogs2466

Hi,recently bought a 1981 xj650. fitted new plugs,air filter,balanced carbs,bike runs good apart from 1 small problem. After about 2 miles when changing gear revs are a bit sticky around 3000/4000 rpm they come down slowly but engine is revlng when changing gear,ok when engine cold but after short run sticky. Removed diaphrams and cleaned needles, slides working ok,throttle linckage returns instantly when cold or hot even after 80ml run ,cold start working fine as well. engine not overheating either.but just this damed sticking all the time after bike warmed up. Can any one sugest why? Many thanks.