So I was laying there in a pool of sweat, feverous due to pneumonia, and started down a path of thinking that disturbed me even in my delirium. You engineers/specialists out there can correct/educate me further in due course.
So I was thinking, in the days before reed valve engines, a lot of fuel went wasted into the expansion chamber and out the exhaust as un-burnt or still burning fuel. In places like California, this was a potential problem with causing forest fires so someone discovered that if you put a metal screen over the end, it would get hot and ignite the un-burnt fuel. Genius in its simplicity really. This small screen kept millions of acres of land on the very brink of closure, open to off-roaders nationwide. But then came the reed valve. This ingenious device in 1974ish eliminated much of the un-burnt fuel flowing into the exhaust. Then in 1980ish came the exhaust valve or "Power" valve. In my mind, these two inventions together should have eliminated the need for the "Spark Arrestor".
So then there was a couple of hours (days, weeks?) I went on about how the spark arrestor is like and afterburner on a jet and wondered if there was any measurable "thrust" and how you would make a machine (dyno) to test it...but that is another story.
So dragging myself back to the original thoughts, I started thinking about why, if I was correct, do we still use this device and my thoughts turned dark. Did I just uncover a government/OEM conspiracy? Every one of us (in the know) knows that government motorcycle exhaust and spark arrestor approval is a racket. There is no (expensive) approval process for auto exhaust, only your states emissions and sound level test, but for motorcycles, there must be the government stamp and for Spark Arrestors, that includes the US Forest Service. To get authorization to use that stamp is an expensive process and your prospective customers HAVE TO PAY IT to ride on public land. Government and OEM's (to include any well funded aftermarket industries) built a business model around it and jumped in bed together. So much money changed hands that it would be silly to stop it just because is was no longer necessary. You know, like wired telephones, NTSC Television, or NASCAR. We, as a people are reluctant to change. (I'm one to talk, I've got 13 vintage motorcycles!)
So here I am, flush and weak, my bed smelling like a gym and me worse, banging on my laptop a small sample of what goes on in my head when most other people floating through time and space, seeing god, or visiting dead relatives.