Signs of a good engine are exceptionally quiet running at tickover, lack of vibes above six grand and an absence of smoke out of the engine breather or exhaust. The same goes for the later, five speed, 45hp version which looks like a larger version of the CD175 and still manages to fly along at a wicked pace. God knows why anyone bothers, chronic top end hassles don't make them a bargain buy even at these prices. It runs very nicely on the road but tends to become a bit finicky after 25000 miles. Burnt exhaust valves, inflammatory electrics and bore wear are things to look for.
Spares are difficult.
Handling's better than the XS650 but suspension ages nastily and the front tyre reacts poorly to a wet, ruined British road. A huge and hugely complex motor, and an excess of mass, makes them a waste of space but the mill is quite tough for the first 40,000 miles and belts out an excess of torque. K One of the twins to survive the seventies better is the old Honda CB350K, a bike that was once the best selling motorcycle in the States. Just enough performance to stop you falling asleep at the controls, classic looks and a simple OHC twin cylinder motor inspired by Honda's sixties engineering. If you want to get really weird then buy one of the old Kawasaki 650 twins.