Tuned Atlas mill in new Isolastic frame could be short-lived if used in flat out mode. Handling went off when Isolastic shims wore, fiddly to set up correctly. Fastback had nasty points, 750S was tuned to 60hp and the Combat made 65hp, went like crazy until it exploded. Thankfully, most of these motors have been upgraded with later Superblend bearings, electronic ignition, etc., but many are still troublesome, short-lived beasts.
1968-73 745cc (73x89mm) OHV twin 56hp, 120mph, 50mpg, 400lbs