1978 Honda CB750F3

While purists and historians will correctly point out that Italy’s MV Agusta released the first 'production' inline four with a disc brake (1966's 600-4) the attention, adulation and technological significance of the Honda Four cannot be denied. Giving credit where credit is due, it is possible the abundance of press and coverage generated by the release of this motorcycle may actually fall short in light of its impact on the industry. As the two-wheeled symbol that ushered in the modern era, there remain two basic and unchanging dividers on motorcycling’s historical time line; pre and post World War II production, and the Honda’s CB 750 of 1969.           

Importing on a world-wide basis by 1970, all of the remaining members of Japan’s big four responded in varying degree to the big Honda. Kawasaki’s profound 900 Z1 was first, upping the ante with dual overhead cams and a clear edge on performance. Suzuki and Yamaha held out longer, releasing a variety of two-stroke models in two and three cylinder configurations, with Yamaha adding to the mix with its version of the four-stroke parallel twin. By 1977, all were campaigning an across the frame four-stroke multi; Yamaha with its shaft-drive XS 750 triple and Suzuki’s brilliant, twin-cam GS 750. Surrounded by gun boats, Honda’s evergreen 750 was showing some brown around the edges, and as the factory was busy developing the new and exciting designs (including liquid cooled V-fours) that would eventually join the GL1000 flat four and six-cylinder CBX, the trademark Four went under the knife for more horsepower.

Like Suzuki’s decision to refocus its GT 750 triple when the RE5 rotary was introduced, 1975's GL1000 tourer lifted flagship duties from the 750 Four, allowing Honda’s engineers to sharpen it more into a pure performance sportbike. Due to customer demand the four-pipe K-model was retained, joined by the Super Sport 750F. With revisions to the exhaust, compression, cam timing and sporty monocoque-like bodywork, the F was an instant hit in both the 750 class and the smaller, but no less striking CB400F. Two years before releasing its own DOHC four in 1979 and needing more competitive power, Honda put the SOHC back on the bench one last time.

The results were impressive. In 1977, the editors of Cycle Magazine wrote: “Honda has hopped-up the F model Super Sport to be just that - a super performer up to challenging anything in its neighborhood. But the 750F isn’t so finely specialized that it loses overall versatility. It’ll  rip through the mountains at handcuff speeds or quietly tour across the continent.” The editors weren’t exaggerating. Displaying the inherent qualities that countless tuners had already untapped, the breathed on 750 found new life in the hotly contested 750 class. In the same test, Cycle’s testers went on to say;“With the introduction of the GS 750 Suzuki, the Hondas were suddenly down a cam, down on smoothness, down on comfort, and performance-wise, down two tenths and two mph in the 1/4-mile. With the 1977 CB750F2, Honda has beaten the dragstrip prowess of Suzuki's GS by a hundredth of a second (12.74), topped it by one mph (105.14) and become so smooth and so comfortable in the process that differentiation would be folly.

Upon closer inspection, the performance of Honda’s 750F2 (and 1978's F3, the last year of 8v production) is even more impressive. Not only was it quicker and faster through the quarter than Suzuki’s twin cammer, the F2 was a full second up on Yamaha’s new DOHC triple shafty and only a few ticks behind the Kawasaki’s original King Kong 900cc Z1 (12.61 seconds). If not for the F2's considerable heft (553 pounds wet) the F2/3 would have outgunned the bigger Kawasaki and flat out embarrassed the GS 750. Not bad for a motorcycle that was all but left for dead in the coming years as the Big Four waged war for acceleration and showroom sales superiority.      

Four Keihin 28mm (now with an accelerator pump) carburetors and modifications to the cylinder head provided the extra push. Combustion chamber and port shapes were altered and the valves enlarged to 34mm (intake) and 31mm (exhaust) from 32 and 28mm. A higher included valve angle made room for .5mm more cam lift while compression was dropped from 9.2 to 9.0:1 due to a redesign of the piston-crown, needed to clear the bigger valves at TDC. The engine’s redline was raised to 9500 and because of the new cam profile, stiffer valve springs were introduced. The 8v also used a screw/locknut for adjusting the tappets instead of the shim/bucket method.  

There was however, a price to pay for this improved performance in the form of premature valve guide wear. A design flaw that only effects the ‘black’ big valve engines of the F2/3 series, Honda’s decision to use the standard rocker arm with the higher included valve angle increased stress to the guides, with some wearing out in under 5.000 miles. Kibblewhite Percision Machining (http://www.blackdiamondvalves.com)  offers a quality replacement which no doubt exceeds the life of the standard guides, but it’s a condition that should be checked often.  

This month’s feature bike was restored by Roy Koch, a retired aircraft mechanic. A splendid example of the F2/F3 series with its triple discs, Comstar wheels and blacked-out driveline, Koch’s F3 looks nothing like it did when he purchased it two years ago. “It had a full Windjammer fairing, luggage rack, crash bars and highway pegs” recalls Koch. “I didn't know anything about the F3's top end issues engine at the time, so the when the seller told me the valve train noise would disappear with an adjustment it sounded reasonable to me. I should have suspected something when he accepted the $500 I offered.” New guides, valves, rockers and a  camshaft later Koch wrestled the engine into the frame, then finished it in gloss black with 750F0-style striping, giving a clean look that suits the bike best. Since then, the Honda has been sold but Koch figures he’ll do another CB750 someday. (<---photo by shabbabear)  

As is often the case and shortcomings notwithstanding, Honda saved the best for the last with the CB750F3. Honda’s ability to transform the 8v from first generation UJM to second generation superbike contender cannot, and should not be overlooked. And while the F3 may never reach the collectible status of the sand-cast 1969 Four, know that what the K0 started, the F3 finished. Nolan Woodbury

For more information on the Honda CB 750, please visit these excellent websites:


http://www.sohc4.net/index.php?q=book/export/html/12

http://www.sohc4.net/index.php?q=content/model-guide-0


Special thanks to Roy Koch. (royakoch@comcast.net) for the photos and information.