From 1956 the C11 was replaced with the BSA C12 which had the same 249cc overhead valve engine in a modern frame with good suspension, more efficient brakes and a more comfortable seat. A number of engine modifications also made it more reliable than the C11. The BSA C12 was in turn replaced by the. BSA C15. However, when the bore and stroke are considered it is actually more like three. C15 engines: the unit-construction T100 has a short stroke, unlike the triple s 67 mm x 70. The major differences were the engine and frame: a double loop with engine mounted at a slant for the BSA and single downtube with engine mounted. The BSA C15 was a 250 cc single-cylinder ohv motorcycle manufactured by the. British company BSA from September 19, and was BSA s first four- stroke unit-construction bike. For most of that period, after the introduction of Learner Laws in 1961, a 250 cc was the largest capacity solo machine that a learner. BSA s earlier 500cc single was the BSA Gold Star, a pre-unit machine with a duplex frame similar to that of the Golden Flash twin. The Gold Star was not considered suitable for the progression to unit construction, and instead the 250 cc BSA C15/Starfire was developed into the 500 cc B50 (via the B40). The dry sump B50.
1968 BSA B25 Starfire 250. The very first Starfires to come into this country had the old skinny seven-inch brake drums on both 18-inch wheels, but that was soon changed to a full-width drum on the front. The frame was little changed from the. C15, though the fork was improved with a double hydraulic.