That is residual from gas additives.
If you use a Dremel to polish it out, wear a mask and don't breath that stuff, really nasty chem.
Get yourself some vinyl mechanics gloves and some masks and do the hazmat work in well ventilated areas.
Some Old mopeds brake pads still used asbestos. Don't use compressed air to blow out the brake linings, use a damp cloth (not oiled) to wipe out the brake linings
Gas/Oil mix that has turned to varnish in the tank and carb is nasty stuff to clean out.
White powdery stuff in carb is gas additive residual