I've disassembled, cleaned the carby, diaphragm and gasket with carby cleaner, emptied fuel tank and cleaned out, replaced with fresh fuel, replaced the jet, reassembled and still no dice.
When I pull the cord the engine must be igniting momentarily? because I can smell exhaust but there's no further cranking, after repeated attempts there's no further ignition at all.
So best bet would be to replace the diaphragm, or entire carby assembly to be sure?