It's not likely to be the carburetor to insulator gasket aussietrev, because that has its greatest effect when the intake vacuum is highest, and that is at idle. Because the H needle has no effect, the problem is lack of fuel supply, so the problem will be a clogged fuel pickup filter, cracked fuel suction line, defective fuel pump diaphragm, or a blockage in the mesh strainer in the pump chamber. You should attend to all of those anyway, before you give it a clean bill of health.
