1970 Honda CB750 K0
Engine: 736cc air-cooled SOHC inline 4-cylinder, 61mm x 63mm bore and stroke, 9:1 compression ratio, 67hp @ 8,000rpm (claimed)
Top speed: 123mph (period test)
Carburetion: Four 28mm Keihin
Transmission: 5-speed, chain final drive
Electrics: 12v, coil and breaker points ignition
Frame/wheelbase: Dual downtube steel cradle/57.3in (1,455.5mm)
Suspension: Telescopic forks front, twin shocks w/adjustable preload rear
Brakes: Single 10in (254mm) disc front, 7.1in (178mm) SLS drum rear
Tires: 3.25 x 19in front, 4 x 18in rear
Weight: 499lb (w/half tank fuel)
Seat height: 31.5in (800mm)
Fuel capacity/MPG: 4.8gal (18.1ltr)/35-40mpg
Price then/now: $1,495/$4,000-$12,000 (1970 die-cast model)
Don Stockett has had a lot to celebrate recently. He not only won an Antique Motorcycle Club of America (AMCA) Winner’s Circle award for this 1970 Honda CB750 K0, scoring 99.50 points, he also managed a narrow escape from road rash on the same bike.
Some weeks before the AMCA Fort Sutter (California) National meet where he won his Winner’s Circle award, Don rode the CB750 K0 in The Quail Motorcycle Gathering pre-show Quail Ride. During the ride, he went a little too hot into a decreasing radius left turn and barely avoided running the bike onto the gravel as the centerstand scraped the pavement. “It’s a big, heavy bike and it’s hard to correct in a corner,” Don says.
Viewed from a perspective of almost 50 years of progress, the single overhead cam version of the 750 Honda is a nice bike with a lot going for it, yet one that could benefit from some focused upgrading. But viewed from the perspective of its contemporaries, the Honda CB750 Four was a revelation. Here was a powerful and reliable motorcycle with good brakes — for the time — a 5-speed transmission, bright lights and an electric starter that worked on cold mornings, none of which were common motorcycle features when the CB750 hit the market in 1969. Just as importantly, the styling was good enough to turn heads, and unique enough to attract buyers.
That Soichiro Honda, the founder of Honda Motor Company, was in the position that his company could design and build a bike like the CB750 was due to years of forethought and investment. In the early 1950s Mr. Honda, with the help of some optimistic banks, bought $1 million worth of American and Swiss machine tooling. Meanwhile, his British rivals soldiered on with the same old pre-war lathes and milling machines — they had to keep the shareholders happy, after all — and Harley-Davidson, then the sole surviving American motorcycle company, had bought up as much surplus equipment as it could after World War II, but years of poor sales had limited its ability to keep up in the factory machinery department.
By 1959, Honda was the largest motorcycle manufacturer in the world. It had based its success on selling small motorcycles of excellent quality to Asian customers, but it soon branched out. As the 1960s progressed, Honda sold increasingly larger capacity motorcycles worldwide. Honda products swamped the British manufacturers’ small bike offerings, and although the Japanese imports cost more, they had good brakes, bright lights and electric starters. And they didn’t leak oil.
The 750 Four debuts
In 1967, rumors began to circulate that Honda was building a 750. Many people thought it would be a twin, like the popular British motorcycles of the time, but when a prototype was exhibited at the Tokyo Motor Show in October 1968, the powerplant turned out to be an inline 4-cylinder. Observers thought the bike owed a lot to Honda’s 500cc GP race bike. Like the racer, the new four had its cylinders transverse to the frame. But where the racer had double overhead camshafts, the street four had a single overhead cam. Painted Candy Blue Green, the new model stirred up international interest and would-be customers jammed Honda dealers’ phone lines, only to be told they didn’t have any 750s and didn’t know when they would. An unknown journalist dubbed the new machine a Superbike — the first recorded use of the term.
American dealers, customers and motorcycle magazines impatiently waited for the new four, which finally arrived on these shores in June 1969. The motorcycle that was imported to the U.S. had one important upgrade from the prototype — a front disc brake. It also had chrome exhausts and a more streamlined tank, although the steering damper fitted to the prototype had been deleted.
Cycle magazine published one of the first full road reports, noting that the electric starter was reliable, the clutch action light and the bike liked to rev, courtesy of four small cylinders and a light flywheel. Vibration was zero, and testers were surprised by mirrors that were viewable at highway speed. High-speed handling was good, helped along by the Dunlop tires, but the rear brake had a tendency to lock up and the bike’s weight had to be taken into consideration when cornering.
Honda’s state-of-the-art tooling enabled the factory to economically produce an engine with a reliable one-piece forged crankshaft, a chain-driven overhead camshaft, a compact 5-speed transmission, and a pressure-fed oiling system. The heads were designed in a sophisticated in-house research facility and Honda’s design team had a computer to assist in number crunching. All this technology allowed Honda to take the 750 from concept to prototype in a very short period. By some accounts, the 750 took less than a year to develop.
As introduced, the Honda K0 was remarkably bug free, but a few items needed to be worked out, including an overenthusiastic chain oiling system that left puddles on the asphalt. Getting the bike up on the centerstand took too much effort, and the clutch was a bit grabby. In general, however, testers were more than pleased.
The one thing that Honda had not taken into consideration was the potential demand for the new four. The first CB750 engine cases and cylinder heads were gravity cast in sand forms. This was a slow method of production, and after the first few months the factory switched to high-pressure die casting. Don Stockett, owner of Vintage Motorcycle Rescue, a vintage Honda expert, explains that only the first 7,414 engine cases — engine numbers to CB750E-10007414 — were produced by the gravity sand cast method, and the rest of the 54,000 1969-1970 CB750s were die cast. A period report mentioned that the Honda factory was working to get component assembly time down to two minutes. In comparison, Harley-Davidson’s entire output of FLHs in 1969 was 7,300 motorcycles.
Good, but heavy
In its March 1970 issue, Cycle magazine ran a shootout between seven top-of-the-line motorcycles. The Honda CB750 was included of course, and got high praise for its excellent (for the time) front disc brake, its strong acceleration and its ability to turn fast laps on the racetrack, but low marks for its weight — 480 pounds with oil but no gas.
Most owners regarded the 750 as a fast tourer, and the reliability of the four became a major selling point. However, drive chain wear was a problem early on, the cause pinpointed to misaligned sprockets and the low quality of generally available period drive chains. Unfortunately, if the drive chain broke, it could break the engine case, and Honda often replaced cases under warranty. In many states, however, the DMV refused to let dealers stamp replacement cases with the original engine number. This is the reason why there are many early 750s with sand-cast cylinders and unnumbered, die-cast cases. Don Stockett has found engine case chain protectors retrofitted to many early machines.
The new Honda caused tidal waves through the motorcycle market. Kawasaki was developing its own big 4-stroke engine when the Honda four appeared, but the project was shelved until Kawasaki could come up with a major improvement on the CB750. It is a testimony to the high standard Honda set that it took Kawasaki until 1973 to introduce the Z1 — a faster, better handling 4-cylinder bike. Yamaha and Suzuki eventually came out with their own 4-cylinder models, similar enough to the Honda to give rise to the term Universal Japanese Motorcycle.
Honda continued to build the single overhead cam version of the CB750 until 1978, and then moved to a double overhead cam version for the 1979 model year. The later Hondas were more refined and comfortable, while the earlier bikes had better lap times. The earlier instruments had plastic housings, which were prone to cracking, while the later ones had metal cases. One major improvement, introduced in 1971, was in carburetor control. The original 1-into-4 throttle cable system made it difficult to keep the carburetors in tune, since the four cables stretched at different rates. The next generation dual push/pull throttle cable system, with a stronger, improved carburetor plate and an improved linkage, helped to keep the carbs synchronized and simplified tuning.
The first-year sandcast CB750s have been collectible for some time. More recently, larger numbers of people have realized how classic most early Hondas are. This is good news for Don Stockett, who retired a few years back, and with motorcycle expert Geoff Sprague opened Vintage Motorcycle Rescue, a restoration facility dedicated to 1960s and 1970s Hondas. In between working on customer projects, he has snuck in a few of his own. This 1970 Honda CB750 K0 is one of Don’s projects, and one he is very proud of. “The Honda 750 was a watershed bike, with numerous improvements to motorcycle design and features. This bike has had such tremendous influence on motorcycle design, and it is still influencing design today,” Don says.
Don decided to find and restore an early CB750, and looked at a lot of possible bikes. After his experience evaluating what he found for sale, he has some advice for other enthusiasts who want their own Honda CB750. “If you are looking for a Honda 750 to restore, you will often find bikes for sale with aftermarket fairings. This is good news. The fairing shields the instruments and the top of the tank from sun fade. Also, people who put fairings on their bikes are usually tourers, and people who go touring park their bike in a garage. They also tend to take very good care of their bike. On the downside, touring bikes are usually high mileage,” Don says.
The bike he finally ended up with, an early die-cast machine, was an eBay find in Tennessee. The seller advertised the bike as restored. “The engine was rebuilt, and it was done well, with a hotter cam,” Don says. “However, he used incorrect bolts elsewhere and left parts out. For example, he left out a rear axle spacer. He re-spoked the wheels, but didn’t bother to rebuild the brakes. The bike wasn’t safe to ride. When I got it, it was leaking oil and would die if I let off the throttle. It had been repainted, but not the right Honda Ruby Red color.
“There is now a considerable premium paid to obtain one of the early sandcast CB750s,” Don says. “The 1969-1970-produced models are identical and are commonly referred to as K0 models. ‘K’ stands for kaizen, the Japanese word for ‘improvement’ and ‘0’ for the first version.” Don is obsessive about details — you have to be obsessive about details to properly restore motorcycles. He made sure all the screws and bolts were correct, and that all the missing parts were replaced. The brakes were rebuilt and the bike was painted the correct shade of Candy Ruby Red. Not content to own a trailer queen, Don wanted his 750 to run as well as it looked. “This is a fast bike,” Don says. “We have raced this bike against a low-mileage, stock bike we have, and it was quite a bit faster.” In 2013 the bike won first place in the Superbike Class at The Quail.
Once a single overhead cam Honda 750 is set up properly, basic maintenance consists of religiously changing the oil. Don suggests changing the engine oil every 1,000 miles. “The engine will do over 100,000 miles without a rebuild. Just change the oil often,” he says. Don also suggests using iridium spark plugs, which are more expensive, but will last for years, and replacing the headlight with a much brighter H4 LED light for safety.
Any vintage bike has its limitations, and Don is well aware of his 750’s. “It’s a great bike in a straight line. At the time, they thought the brakes were great, which shows how bad the drum brakes on all bikes of the time were. Careful attention also needs to be paid to the battery. The charging system is just adequate to keep the battery charged. It won’t run the lights and recharge the battery. If you ride the bike with a very low battery, the alternator will funnel full charge to the battery and eventually burn out the alternator. Keep your battery on a trickle charger to keep it fully charged for riding,” Don says.
“It’s got a wide seat and large side covers, so it feels bulky, but solid. It’s also hard to correct the line in corners, especially if you go in with too much speed. But the seat is very comfortable, and it doesn’t vibrate. It’s a good freeway bike, and with a fairing it’s almost as good as a Gold Wing. Just keep in mind that it is not a sport bike, so be careful and ride conservatively. The 750 will require your attention at all times. It has incredibly beautiful classic styling that everyone recognizes. It sounds wonderful, particularly with the early HM300 mufflers. I never get tired of hearing the sound out of those pipes.” MC