Olev,
I wasnt sure how to go about putting a explanation about cams into words so I will quote from D.W. Munro's book of BSA twins.
Quote - "Officially there are three "A" camshafts: that fitted to the original A7 and Star Twin up to 1951 (67-695), the A10 camshaft also used on present day A7 models (67-334), and the sports camshaft (67-356) for the Star Twin, the Shooting Star, and the Road Rocket.
When dealing with compression ratios we stressed the importance of having cams to suit the ratio. A high compression engine works harder than a low compression one: it develops more power, and to do this it must be able to breathe more freely. The cams therefore usually have higher lifts and longer periods. They also have more overlap, which means that the inlet opens earlier and the exhaust closes later, so that there is a longer period at the appropriate top dead centre during which both valves are open at the same time. This has a profound influence on the extractor effect, which is discussed further in the notes dealing with exhaust systems.
To sum up these remarks, it simply means that sports cams are necessary for the sports performance expected of high compressions. If ordinary cams are used the engine will be stiffled, and consequently unable to give of its best." - end quote.
Your bike being a Star Twin would have had a 356 cam in it as standard.
Hope this is of some help.
Brian.