Did you pull the dip stick and check the
oil? On a similar problem, my son said he knew it was full of
oil, as he had just filled it, and wasn't stupid. I said humor me, I'm old. Pulled the dip stick to find a gallon of gasoline in it. Seems that new diaphram fuel pump had a hole in it. You could have water or other issues.
If when spinning with the drill the pump turns freely (no load on drill) and you don't see
oil flowing out the gallery plug, I think I would suspect a pick up tube problem.
Do you have any shop rags missing? A friend found out that the rag is too fine a filter for the pickup tube.
Good luck.