That is probably from rust in the tank, it is not uncommon to introduce particles into the fuel system when changing a fuel component (fuel pump in this case), if you have very much rust in the tank the sock may be plugged. And that stuff may have gotten into the carb, also. Some fuel filters have a spring inside to push the filter away from its seat if it becomes plugged, I'm not sure if the clear ones are that way. I would do a fuel pump capacity test, disconnect the fuel line from the carb, put a piece of flexible fuel line on the end of the line and put the other end into a quart metal can, ground the coil hv wire to the block so you don't get a spark, and the motor won't start, then crank the engine for 20 seconds, you should have at least a pint of gas in the can, also look at the color of it, rusty, water, etc. Good Luck.