This is after I assumed they were clean...

I think that an inspection of the fuel filter and tank is in order. It looks like dirt. Is it rust?
In reply to pilotbraden :
It was in aluminum float bowls, no steel to be found. Gas tank was cleaned to look brand new but I sold it and am buying a brand new tank. There was only a tank petcock filter which went with the tank.
Never assume since you drained the bowls, they’re actually clean!