For almost fifty years I have neglected to address this issue. I assumed it wasn't necessary. Everyone knows about this, right? But this week I discovered that even powersports industry voices that are nationally known and respected have dropped the ball on this. It's so simple that it is amazing that no one is talking about it. And certainly not motorcycle user forums. But then we could hardly expect them to.

I'm not sure how the other brands do/did things, but Honda during the period of the single-cam fours designed the exhausts for these bikes with a technology they called "gradual expansion". This meant that instead of sound absorption by fiberglass or other soft materials as many exhaust manufacturers used, Honda was known for using exclusively or predominantly an all-metal baffling system. Even where fiberglass was present, they still relied mostly on metal baffling. The energy of the exhaust gases dissipated as it encountered each successive wall inside the muffler, flowing from compartment to compartment, and the sound level dissipated with it.

So the exhausts had good sound control, but at the same time, they were heavy. They were well known for this. Infamous even, as aftermarket replacement exhaust makers capitalized on this and claimed significant weight savings. There was a lot of metal mass in these stock Honda exhausts. However, all this metal resisted warming up on engine startup, the result being that the moisture produced by combustion didn't always get evaporated out. And with the acidic nature of this water, corrosion formed quickly inside the muffler. And guess where? At the weld seams and at the compartment walls. There are many fifty year old Hondas that show bulges circumventing their mufflers. These are the baffles growing larger with rust's accumulation and pushing outward on the exterior of the muffler.

But this can be prevented. It's simple. Never start the machine without putting a few miles on the bike to fully heat the exhaust mufflers. Even if there is snow out, if I start the engine for any reason, I will turn the idle up slightly and let the engine run for about ten to fifteen minutes. That is, until the muffers are hot enough that they are uncomfortable to touch. This is probably not as good as riding the bike, which gets the mufflers the hottest, but it basically does the job. You will notice something here, I hope. That thing many recommend of starting the engine every so often to "keep the carbs clean" is a really bad idea. First, it will not preserve the carburetors. And worse, it will trash your exhaust.