1968 BSA Spitfire MKIV 650cc Motorcycle

Description

One of the oldest British motorcycle manufacturers, the Birmingham Small Arms Company began building bikes with proprietary power as early as 1903 and by 1909 were using their own engines, starting with a 3.5 horsepower belt-driven single.  BSA went on to become one of the most successful of all British manufacturers, both on and off the track, building a diverse range of bikes through the 1920s and 1930s that kept the company alive during the Depression.  A development of the successful A10, BSA’s new range of A50 and A65 twins took advantage of unit construction to modernise the packaging of the engine and gearbox in the late 1950s and would remain in production from 1962 until BSA finally went under over a decade later.  The two models shared many parts, including the stroke of 74mm, with the 500cc A50 having a bore of 65.5mm and the larger 650cc A65’s bore 75mm.  With a new frame came a new name, the so-called “Power Egg”, a reference to the design of the new unit engine and gearbox.  The A65 was sold in a myriad of different versions, including the Rocket, Thunderbolt, Lightning, Spitfire, Hornet and Firebird, and was steadily improved over the years.  Answering the call from American customers for more power, the Mark II Spitfire of 1966 (there was no Mark I) boasted twin big-bore Amal GP carburettors and a compression ratio raised to 10.5:1 for a claimed output of 55 horsepower and 120mph top speed.  An updated Mark III version was launched in 1967 with Amal Concentric 932 carburettors, larger fuel tank and reduced compression, followed by the Mark IV of 1968 with a twin leading shoe front brake and independently adjustable Lucas ignition points for more reliable starting and easier tuning.  Built for one year only, only 1291 Mark IV Spitfires were completed and they rank as one the most collectible of all BSA motorcycles.