The CB750 Prototype

This is the CB750 Prototype story as told in a Japanese motorcycle magazine and in photos of the bike and owner, Robert Brooks of California. Later information suggests that this bike is a modern replica of the prototype bikes that made the rounds of west coast dealers in 1968. Whether it is or is not, the article and the photos of the bike are an item of interest, so they are displayed here without any claims to authenticity. Thanks to Joe Broussard for providing the photos and the article; and Munekazo Shimizu, SOHC/4 #256 for the translation.

  1. In California, USA, a CB750 four prototype was reborn. The most remarkable difference is a CB450 K1-like fuel tank, by the way, a fuel cap is a same easy-open-hinge type which was used for mass production CB750s. A color scheme is close to well known Candy bluegreen. Mufflers don’t have a curved seal, HM300 and also #4 header pipe is without the dent for rear brake pedal. A whole image is somewhere between the first export model (sand cast K0) and a 1968 prototype.
  2. A turn signal switch unit is beautiful polished aluminum without “TURN” on the unit. On the other hand, K0 has a painted one.
  3. A steering damper on the top bridge gives the meter panel a fresh view. The speedo has up to 150mph on its scale.
  4. A steel brake pipe comes out straight from master cylinder unit. On the other hand, K0′s oil line goes down at right angle with banjo joint. The shape of the Kill Switch is slightly different from K0, and switch doesn’t have “On” in the middle.
  5. A plastic throtle free adjusting nut. K0 has ordinal metal nut.
  6. A brake caliper doesn’t have holizontal cooling fins on it. On the back side of the caliper, there’s no curving to lighten the weight of the caliper. This was seen on another prototype introduced in 1968.
  7. A friction-type steering damper is installed down below the head pipe. According to lots of pics of other prototype, the damper was usually a rod-type. Needless to say, the bike also has a hole on the steering stem and a stay on the main frame for future installation of the damper.
  8. A seat, so called “Red Supo”(?), is the same type on K0.

No translation available.  If you can provide a translation, please email it to me at


Robert Brooks, running a motorcycle shop called Bikesurus near Los Angeles, California., is a real motorcycle enthusiast. Early Japanese multi-cylinder bikes, such as CB, Z, etc., in his shop are the proof of his passion to motorcycles.

One day, he found a strange CB750 four at the junk yard by chance. The CB wasn’t in good condition, however, he had never seen the kind of CB before. Sure, the CB he saw is a rare prototype CB which usually can’t be survived for a long time. He did know about the prototype CB introduced in 1968 by one of the Japanese bike magazine. He also saw the picture of the prototype-CB with a CB450K1′s fuel tank for camouflage running on test track in Tokyo, Japan. Holly s***, the bike was then in front of him! He of course started negotiating with the owner of the bike. However the owner was die-hard if he knew anything about the bike or not. After lots of visits to the junk yard, he finally could manage to get the prototype-CB.

According to Brooks, he restored the bike in stock condition with 99% genuine Honda parts. Of course, he did use bolts, well-known among CB enthusiast, with punched seal ” 8 ” on its head.(??) Also a color scheme and some other details were completely restored in original condition. The most interesting point on the bike is that the bike is made up with both special parts for the prototypes and regular parts for K0 and later.

Honda News, July 28th, 1969, says that Honda started to export CB750 four to the U.S. in April, 1969. Another information in the states says it was July in 1969 that all Honda dealers in the U.S. got ready to sell CB750. In fact, the prototype-CB has its original title registered in June, 1969. In Spring, 1969, Honda already introduced a K0 to the Japanese press, and this means that the style of K0 was completed by the time. Brooks assumes that the bike was used for the pre-sales-demo to major Honda dealer in the U.S. according to his own research. However, the truth is still unknown. By the way, in 1968, when Honda started the development project of CB, the prototype was actually tested in the U.S., too. Because the U.S. is Honda’s main target market outside of Japan. Soichiro Honda got all control on any motorcycles made in 1960s. Whenever he thought any change should be made, he did make it, even a bike was under development or just before the shipping.

About the picture: Early prototype is running on the Arakawa test course, Tokyo, Japan, 1968. Fuel tank and F & R drum brake is from CB450K1. In Oct, 1968, just before Tokyo Motor Show, Honda decided to install a front disk brake on CBs. There is some testing devices on the fuel tank. A cowling was also tested. This tells the potential of CB was really high.


We assume that this CB is exactly one of the prototypes which is born during the CB development. Brooks’ shop, Bikesurus, has a close connection with some bike shops in Japan. Bikesurus plans to have a Japanese brunch next year. He will display his prototype-CB at the Classic & Custom bike show in Tokyo starts from Jan 22. Some CB funs already asked him to sell the CB but he doesn’t want to sell the bike to a private owner. He really respects Soichro Honda, and believes that the prototype-CB should be in a Honda’s collection hall in Suzuka, Japan. He also thinks this is the best way that he can do as a one of Honda CB enthusiasts.

Top Picture:
  • Left: 1968 Prototype
  • Right: 1969 CB750 four (K0)

Code name, HM300, so called K0, was developed within a year!!! During the development, lots of prototypes might be born and disappeared…

Who the heck registered the bike? Date is June 16th, 1969. American Honda, Honda or a dealer? Anyway, the bike has enjoyed a quiet life in California. Robert Brooks is the third person from the left in the bottom picture.


Robert Brooks, third from left, is shown with the staff of the Japanese magazine which featured this article.  The bike had been shipped over to Japan at the time as Mr Brooks was seeking to learn more about the authenticity of this motorcycle.