The guy porting my head (and assembling my engine) rang to say the bolt-in inlet stubs on my K6 head could not be opened-up enough to accommodate my 31mm (kit) Keihin smoothebores. He says the walls of the standard manifolds would be way too thin. He suggests removing them and welding in specially made stubs onto which the standard carb. rubbers will fit. Has anybody encountered this before? Also, Cycle - X say that 1977 - 78 intake rubbers give better performance than the standard ones (16211-300-030 and 16212-300-030). I'm not sure what model this refers to but presumably F2? K7? (16211-405-000, 16212-405-000, 16213-405-000 & 16214-405-000). Anyone had experience of this?