I had a CB 650 custom of about that era (81 or 82 ?). Same 4 cyl air cooled engine as the 650 nighthawk. In general it was a great starter bike. It had a low seat height and center of gravity, had enought grunt not to be a dog, and was a comfortable riding position for around town. If you were gonna do much highway riding, you'd want either a small windshield or a bike with a bit more forward leaning riding position to be more comfortable.
I didn't have any problem with the engine... they were prone to have some small oil leaks at the top of the valve covers, but all the advice I got at the time was to just live with it. That's how they all would end up in short order if you re-sealed them anyway (so I was told).
If you do look at one, the typical problems were the 4 into 4 exhausts rusting/burning out right about the level of the pegs. (they had a low spot there and condensation tended to sit there) I put a 4 into 1 header/pipe on mine, not for the performance increase, just because I got a great deal on it, and mine stock pipes were leaky. The real benefit was the about 40 lbs of weight the bike lost! (heavy exhaust and center stand had to come off)
Mine really ran exceptionally smooth after a tune up (which I had done too infrequently). With 4 carbs to be synch'd etc, it's likely anything you'd buy would benefit from a tune.
If you're taller than 5'10" you might find the cb650 or 650 nighthawk to feel a bit small for you. For longer trips it was sometimes nice to put my feet back on the rear pegs.
Oh, last thing, my advice would be that whatever bike you buy, it would be a good idea to buy one that has "crash bars". They're the bars that bolt on the frame and are just a little wider than the engine. They're not meant to do you any good in a real crash, but they protect the engine cases, shifter and brake pedal in event you drop the bike (or some dork knocks it over when it's parked).
Even if you're careful and a good driver there is a high probability that your bike will lie down at some point or other. (mine was knocked off it's stand a couple times, and had the blacktop give way under the stand on hot days a time or two). I saw a guy drop a Seca (I think??) once, it broke the left side gearcase in 2.. he stood scratchin' his head while it leaked all the oil out. Oh, and some Seca's (or all?) were turbocharged... I'd steer clear clear of those for your first bike. A friend had one (a good rider) and he said the turbo lag combined with driveshaft lift on the rear could make some interesting things happen in corners, when driven hard.
Anyway, there's some more feedback for ya anyway!!
Brent
