Is it the tach or signal?
On the engine, starboard side are 2 voltage regulators. Each has 2 yellow wires (AC from stator), red wires and a gray wire. Swap your tach signal wire to the other reg gray wire. If your tach still does not work, your tach itself may be dead. Very hard to find that 2" tach. I opened the hole in my dash to take a standard size tach. Easier to read, too.
About your exhaust hose- look for a brand name on the hose. i know the hoses have a slight bend in them. Can you use straight hose and rotate the muffler slightly?
