the risk is it runs through your TB's and through the combustion chamber, scoring so forth, some could get in crankcase as well, best to flush it out if you see any signs of it while draining oil and inspecting filter, a good engine flush.. enough of it could wear down the nikasil coating on the cylinder, don't want that..
what's the history of the bike where did it come from? what are the chances the bike went down in a sandy area? I went down in death valley like a 2 dollar whoore, the turn had a perfect runoff of light pumice and sand, very nice... however I was picking sand and rocks out for years.. seemed every time I went to service something I found evidence of this incident, and I did find it up in my air box as well however the light coating of oil inside the box trapped it, or most of it some may have gotten through? I just cleaned the box well and went with it, no internal damage at all I was aware of, good compression ran like a raped ape..
I suspect the sand was thrown up by the front tire on the lowside engine revving fairly high sucked a bunch in then the bouncing around dislodged the air filter momentarily and that's how the sand got in, it's the only place I ever rode where there was sand?
that's a very glassy sand where could that have came from? white sand? do they do the roads where the bike came form with white sand? is it from the southwest where the bike may have been caught in a sand storm? very clean sand I'd rule out winter road sand, usually sand from winter ice is dirty and nasty.. this looks more like beach sand or a wind storm sand say around white sands area? bike from new mexico by any chance?
whats the filter look like? there is a good chance this is old sand debris from a former crash of some sort or a sand storm and when they removed the clogged up filter some fell off and it wasn't cleaned up? sabotage?
or as someone mentioned already someone ran the bike without a filter or one with holes in it? might have to call the pink panther for this one... in any event check out what ya can, oil, maybe filter the oil for giggles, clean it up and go with it, if you are real worried you can do a compression test and or a borescope and inspect the walls what not, that sand should get powdered up fast enough if it is indeed sand, but you really don't want it anywhere near the intake... if it runs fine clean it up call it a day.. change fluids shake out air filter so forth.. suck it out from the other side to pull out sand what not..
oh and suck it out of the TB's with a vacuum cleaner I can see sand sitting on the butterfly valves.. tape up a long fat straw on your vacuum cleaner hose and get as much out as possible, then rinse with a cleaner.. don't want the sand doing any sort of mechanical blocking or whatever, holding a butterfly valve open more on idle what not get it all cleaned up real good..
if you look at the second pic you posted the TB closest to you the brass butterfly has sand all over it as does the TB and the rubber sand can hold the butterfly open and throw your TB sync out of whack.. crush some of that sand with a hammer does it break down easily?
