"Stormin Mormon" wrote in message
...
Very likely air in the line. When you pour ten galons into a
275 gal tank, the liquid fuel covers the inlet tube by about
0.00001 inch. When the furnace pump comes on, it's really
easy to gulp some air. After you get your tank of heating
oil delivered, it should run better.

Probably stirred up a bunch of crap and sludge on the bottom too.