Got my mower back. Was about $180 worth of repair time to clean out that crap. They cleaned the tank, which had to be wiped out....wouldn't just rinse out. The fuel line up to the fuel filter was full of it. Replaced it. Fuel filter was clogged and replaced. No trace in line above fuel filter or in carb. Fuel filter was so clogged that no gas was getting through.
Mowed Friday night and it ran great.
Just to clarify, the contaminant particles were very very fine, despite how the pic looks. It was not gritty like sand but very fine like talcum powder. So fine that when dried out it clumped together to look like it was larger particles.
Also, there is no question that it came from the gas station. It was in all of my cans and they went right from the gas pump into my mower. I think the gas station tank was down to the bottom and the very fine particles were concentrated.
The dealer says my truck's filtration is much more robust than on a mower and nothing would have got to my injectors.
I'm not going to bother trying to get the gas station to pay my repair bill. 4 cans (20 gal) is about what I put in my truck when I fill up anyway—so a receipt only proves I bought gas, not that it was contaminated. And, I don't need the frustration.
I'm back to mowing so I'm happy. I bought 4 new cans and filled up at a different place. Since this happened once in 13 years here, I'm not going to worry too much about it. But I will keep a close eye on my fuel filter.