is it the same principle as a scooter with a semi-automatic transmission. In other words is it shifted electronically or manually as you would with a traditional clutch ?
James is right on with the description of the transmission. Two speed, left foot shift, shift as you wish, no clutch. If I remember correctly, the right lever was the front brake - as normal. The left lever (normally the clutch) was the parking brake, locking the front wheel. It was purposely set up to need two hands to avoid accidentally setting the brake.
The 400-450 has a left hand lever that is a parking brake for the rear wheel. The 750 has no lever on that side at all and the parking brake is a lever or knob (can't remember exactly). You depressed the foot brake and then activated the lock. The torque converter is more or less the same unit used on the Honda Civic cars of that era. The 400-450 is a great bike to learn to ride on, although pretty slow in acceleration, not much faster than conventional 250-300cc bikes of that same time, although they have way more mid range torque, meaning you can power up hills much easier. The first 750 Hondamatic had a 4 into 1 exhaust while the later one had a much better looking 4 into 2 exhaust, more pleasing shaped tank and the blue ones were beautiful. However, while the later ones had a more comfortable looking seat, it wasn't. They are also rather slow, but much faster than the 400-450. They have plenty of mid range power, making passing no problem. They also get great gas mileage, making them a good touring bike.
The Hondamatic motorcycles (CB400 and CB750) had a two-speed semi-auto transmission with a conventional foot-operated shift lever. You shifted when you chose, and there was no clutch lever. The front brake had a locking mechanism on the lever, so that it could be used as a parking brake. The bikes could move off from a stop in either gear (just twist the throttle), but were especially slow to accelerate in 2nd.
