Ah, it makes sense now.
Anatomy of a rust particle. These things look like jagged little 3D puzzle pieces. Very tiny ones break off and can fit through the screen in the early 70's Honda petcocks. Once they make it to the carb bowls they either get sucked through the engine, if it is running, or settle to the bottom. This is where several of these little buggers get together, interlock their puzzle bits, and look for more to join the party. When the colony gets big enough, they become flakes. (There's a joke lurking here some where, but nevermind that now.) Anyway you jump on the bike, tool around and hit a bump that dislodges that rust flake at the bottom of the carb bowl. If it's jostled over to the main jet while you're on the throttle, whosh, through the engine and out the exhaust. Ah, who cares. But, lets say the flake gets jostled over to the tiny pilot jet orifice, and can't fit through? What if several of these flakes try to get through and wedge themselves into that tiny orifice. Now, that cylinder gets little or no fuel when you back off the throttle at the stop sign/light/whatever. This usually ellicits the, "What the F**K?", response, because the machine either dies or has a fraction of the power you've come to expect. And why? All because of a bunch of tiny flakes!
Cleaning the carbs will correct the problem short term.
Adding an even finer fuel filter will mask the problem until it, too, cloggs up.
Cleaning, and perhaps coating the inside of the tank, will correct the problem for several years.
It all depends on just how much you can tolerate flakes.
Cheers,
