 This engine did not prove popular with all operators, being prone to poor fuel consumption and heavy smoke production if not maintained to high standards.Some operators experimented with a different engine and found they could avoid the 510, which had the reputation of being a high maintenance unit and hard to work on.Later on a simplified model (10351B/1R) was offered, with an engine that was reduced in power to 150bhp instead of the usual 180bhp setting for the heavier duty version of the National.