The original Honda CB1-400 was only available as a grey import, mainly from Japan. Japan has a licensing system that favours 400cc bikes, hence there is a large market for this engine size over there, the vehicle requirements (our MOT if you like) make it hard for old bikes to survive out there, hence many a Japanese spec 400cc bike comes to our shores.
What do you get with a CB1 then? What about a Naked CBR400, the same rev happy 54bhp screamer of a bike with a low seat height, handling to make a CBR600/GPZ600/R6- In fact any 600cc sportbike owner cry with anguish because they simply cannot keep up on the twisty bits. It has a surprising turn of speed too, although limited to 180kph (about 112mph) this limit can be disabled by simply fitting a kilometer to miles speedo converter as supplied by Motrax for about £30.00, this allows 12,000 rpm in top- about 122mph. The only real disadvantage is the lack of wind protection, making it a contest between wind and your arms over 80mph, but a simple cheap screen can do wonders for this.
What you will usually find is a low mileage bike, that has probably been stood a while, so you need to hear it start and run from cold. The front brake is more than adequate for the weight, and it is a light bike. It has a tendency to run hot if there are any air leaks in the inlet tract too, so don't remove the air filter! And the spark plugs are dear at £8.00 each, other than that, they are great fun easy bikes to live with. I've had two, so I should know!
There is a later model for sale, called the CB1 Super-4, different bike, much larger, not as quick but it does have wind protection in its favor.
Be warned that the tank is not very big, and if you use the performance you will need fuel every 120 miles, but my steadiest riding produced well over 60mpg, my worst (trackday) 30mpg, so you squeeze the twistgrip and make your choice.