in your map, right click. then go to fx > fx_runner.
then, with the fx_runner entity selected, press the "N" key.
then, in the box at the bottom where it says Key, type in "fxFile". Make sure it is exactly like that. (without the quotes, of course)
Then, in the box labeled Value, type in "spark" (once again withoit the quotes)
And thats it! You can use another effect file from the assets0.pk3 file, if you want. here are most of the sparks:
i think thats all of them. i hope this helped