So I called Terry at PT and explained my glowing exhaust. He explained that the kohler motors heat up the exhaust until glowing, and most folks don't notice until they operate at night. He didn't seem concerned but just in case, he gave me a number to a Kohler Tech. The tech asked if just the headers were glowing or the whole exhaust. He said headers glowing is normal, but the whole exhaust muffler should not heat up that much. He suggested a number of things:
1) Exhaust manifold gaskets leaking air
2) Woodruff key on flywheel sheered, affecting timing
3) Fuel solenoid in carb not opening all the way
4) Carb set too lean (not adjustable)
5) Fuel pump not pumping enough.
So I'm looking for manifold gaskets, with little luck, but I don't see anything that would indicate a leak. I pulled the fuel shut-off solenoid and touched it to 12v, and it is working fine. I cranked the motor with the fuel line disconnected and was rewarded with strong pulses of fuel - I replaced the fuel line for good measure. I don't suspect I can check the flywheel without pulling the motor though. Here are what my plugs look like - best I can tell they look like the "normal" picture when you google image "how to read a spark plug."
So I really don't have a plan moving forward, except trying to find new exhaust gaskets / studs / nuts. I am questioning if I even have an issue, or if the exhaust glowing at night is normal. I don't really want to find out by hosting a huge fire behind me as I'm pushing snow.
Thoughts appreciated.