A small change in the amount of oil delivered to the motor would not make a significant difference if fuel milage.More likely something was adjusted or changed which made the difference, plus you have to account for the extra oil used during the automatic break in.
One thing that affects milage and oil consumption is having a propeller that does not allow the motor to turn up to its optimal rpm range. Most fuel economy or excessive oil usage complaints are propeller related. Your 250 HO has a 6000 rpm redline but an optimal WOT rpm from 5500-5800 with a normal load onboard.
You say you have a 250 HO, that model does not have a reduced oil setting because most of the later HO models are used in high performance applications which needs addtional lubrication protection.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.
Good Evening Gasman:
Your 250HO does not have a XD100 setting on the computer. You should run XD100 as it is the very best oil for your engine but again, your EMM on the 250HO does not offer a choice between TCW3 & XD100. The only setting is TCW3.
The 250HO is one impressive engine!!!!! Just make sure you have it propped correctly as BluewaterBill outlined in his replay to your question.