In early 1933 a modified version of the engine was announced that had improved valve timing and only two carburettors but the output was up at . This engine was called the KB and the previous version, which continued in use, the KA.
In January 1933, an improved engine design featuring better valve timing and just two carburetors was unveiled. The power output went up to . This new engine was named KB, whereas the older KA continued to be used.