Here's an old hot rodder's trick that seems to be working well for me:
Each time I pull the lower cowling off for any reason, I coat the entire exhaust system from the exhaust ports at the cylinders to the end of the tail pipe with automatic transmission fluid, including the muffler and springs. An old shop rag works well to smear a liberal coating of the stuff. Leave it wet, but not dripping.
When the engine is fired up and the exhaust system comes up to temperature, the automatic transmission fluid just seems to go away, leaving a gorgeous burnished copper/brown finish on the entire system. No surface rust.
Each time I pull the lower cowling off for any reason, I coat the entire exhaust system from the exhaust ports at the cylinders to the end of the tail pipe with automatic transmission fluid, including the muffler and springs. An old shop rag works well to smear a liberal coating of the stuff. Leave it wet, but not dripping.
When the engine is fired up and the exhaust system comes up to temperature, the automatic transmission fluid just seems to go away, leaving a gorgeous burnished copper/brown finish on the entire system. No surface rust.