You may also wish to place a wooden block over the tube's end and give it a couple of 'fraps' or slight but firm taps to help break the bond and also acquire a small plastic handled 'strap wrench' sold by plumbing supply companies to protect the finish on polished fixtures. The strap wrench can be quite handy removing recalcitrant choke tubes as it provides more leverage than the average factory choke tube wrench and will not mark or distort the tube.