LE velocette start

1964 Ex-Metropolitan police L.E. Velocette engine.
After much panting I got her running. Left hand cylinder head has a leaking gasket due to a corroded water jacket port. I needed to advance the ignition timing several degrees becuase modern fuel has a much higher octane rating than the fuel around when the engine was design. Trouble with the kick start returning correctly. A common LE velo problem.