In 1890 the most important source of revenue for the federal government was?

Income tax

*edit* I don't think so. Perhaps in modern times, but income taxes weren't even considered constitutional until the sixteenth amendment was ratified in 1913. It was used as a considerable source of revenue around WW2, and it just sort of stuck around after that. In 1890, I would say custom duties (tariffs) were the main source of federal revenue.