My two centavos

Kevin, The comments above are very good and accurate. One problem is engines go in and out of being good steamers when they are receive heavy repairs. #484 is my favorite locomotive.It always steamed well for me on both side of the cab. However, I heard back in the day she was a poor steamer for a while. After decades of wear and repair engines indeed aquire their own characteristics. Some engines, however, could never shake a reputaion as a poor steamer.In those cases there is something big wrong with the drafting.
Changing fuels burned by a locomotive can definitely affect steaming, but this can be remedied by modifying the front end baffling. Converting to oil is a big deal, and aside from installing a burner, holes need to be cut into the "petticoat" pipe extension from the stack.
Poor steaming is generally defines as an inability of a boiler to keep boiler pressure and an even water level while working upgrade, as fuel and water are being steadily added to the boiler. Poor draft is a usual suspect. Sometimes just a row of plugged flues can contribute to poor steaming. Sometimes there is a problem in the front end baffling. Even new tires can affect steaming as they bigger circumference slightly lessen the number of exhaust beats, and therefore the draft on the fire.
Poor steaming engines can be dealt with as long as both the enginemen are paying attention. An engineer can really help if he works the cutoff and the throttle till a the consumption is balanced with the boiler's ability to produce steam.