Not to argue, but the 22R I cherried the manifold on was fine after richening the mixture. Running a rich mixture can cause fuel to burn in the exhaust, but usually that only makes a popping or backfiring sound and doesn't really create any more heat than is already there. Excess fuel will "wash" a cylinder causing it to cool. Hence the reason Harley's ignition modules will shutdown cylinders when the temps get too high. No spark no fire, cool fuel washes cylinder, reduces temps, bike stays running (although a bit rough and slugish) and nothing warps. fuel burning in a manifold isn't hot enough to cause the manifold to heat up to cherry red. It's no longer compressed once it's pushed out the exhaust thereby making temps lower than in the cylinder. Lean however will superheat the air left in the cylinder and blow it out the exhaust causing the manifold to heat. Heating the manifold and the internal cylinder temps causes the engine to run hotter in general and I've even seen it burn holes in pistons, melt valves and deform exhaust headers. Perfect example of too much air not enough fuel and the effects on metal. Look at an Oxy/Acetylene cutting torch. regular mixture heats the metal, but as soon as you hit that extra oxygen it melts and blasts through it. The Acetylene is the fuel, the oxygen helps it burn just like gas in a cylinder. You increase the amount of oxygen over the amount fuel and it get super hot. Anyhow, sorry to ramble.