The Smallest Four: Honda CB350F

Honda’s magic shrinking act gave us the smallest production version of its inline four, the CB350F.

| January/February 2012

CB350F Left Front View

Honda’s CB350F was the smallest version of the well-received Honda CB750.

Photo by Rick Schunk

1973 Honda CB350F

Engine: 347cc SOHC transverse-mounted inline four, 47mm x 50mm bore and stroke, 9.3:1 compression ratio, 34hp @ 10,000rpm (rear wheel, estimated)
Top Speed: 98mph (period test)
Carburetion: Four 20mm Keihin
Transmission: 5-speed, chain final drive
Electrics: 12v, coil and breaker points ignition
Frame/wheelbase: Single downtube steel cradle frame, 53.3in (1,354mm)
Suspension: Telescopic fork front, twin shock absorbers w/adjustable preload rear
Brakes: Single 10in (254mm) disc brake front, 6in (152mm) SLS drum brake rear
Tires: 3 x 18in front, 3.5 x 18in rear
Weight (dry): 373lb (169.2kg)
Seat height: 31in (787mm)
Fuel capacity/MPG: 12.1-liters (3.2 gal.)/40-60mpg
Price then/now: $1,100/$800-$3,000

Magicians like David Copperfield and Criss Angel stun and amaze audiences with their mind-bending stunts and tricks. While Honda isn’t generally recognized as a magic act, the company did stun and amaze the motorcycle community in 1969 when they introduced the CB750 Four — the first in a new generation of quality, oil-tight, large displacement multi-cylinder machines. And while they started big, Honda still had a couple of other tricks up its corporate sleeve.

Two years later, in 1971, Honda introduced the smaller CB500 Four. Cycle Guide magazine thought the CB500 was quite the package, as its August 1971 issue headline blared: “They’ve Done It Again: Honda has unleashed another new standard for the motorcycle industry to follow.”

If that wasn’t amazing enough, Honda’s next magic act was to decrease the size of its four-cylinder engine package even farther. In the spring of 1972, Honda introduced the CB350F. “Honda had blown everyone away with the 1969 introduction of the CB750 Four,” says Honda enthusiast and collector Doug Sheldon. “In 1971, the CB500 Four was released, again ‘one-upping’ all the competition. So the 1972 release of the 350 Four was almost a natural progression — a statement as to what Honda engineers could do.” The world’s first mini-multi, it was the smallest capacity multi-cylinder motorcycle to ever enter into full-scale production.

Through the years

Honda had, of course, been developing the multi-cylinder power plant over many years, with experience gained in both their motorcycle racing exploits and their efforts with V-12 Grand Prix formula racing cars. By the time they introduced the 350 Four in 1972, the design and layout of the Honda SOHC four-cylinder engine was well established, helping coin the term “Universal Japanese Motorcycle,” or simply UJM as the basic layout was called.

In the Honda CB350 Four, this meant a transversely mounted four-cylinder engine featuring a chain-driven single overhead camshaft. Crankcases were of the clamshell type, split horizontally to allow easy assembly of the unit-construction gearbox and the five-plain bearing crankshaft. Primary drive was by chain, taken from the center of the crank to an inboard-mounted clutch. The 350 Four engine is undersquare, meaning the 50mm stroke is longer than the 47mm diameter of the bore. And at 47mm, each of the four pistons is not much larger than a medium-sized plastic pill canister you get from the pharmacy.

4/22/2016 10:46:16 AM

The article includes the statement, “The world’s first mini-multi, it was the smallest capacity multi-cylinder motorcycle to ever enter into full-scale production.” This isn’t actually the case. At least two other manufacturers mass-produced even smaller multis in the 250cc class. The same year as the Honda CB350F made its debut, Kawasaki rolled out its own mini-multi—the S1 250cc triple. That bike remained in production until 1980, though its designation was later changed to KH. Then, in 1978, the DeTomaso Group in Italy began production of another mini-multi that was smaller than the CB350F, marketed under the Moto-Guzzi brand as the 254 and under its Benelli brand as the Quattro 250. It was a 250cc (actually about 234) SOHC four cylinder four stroke—rather a Honda clone in some ways as far as the engine was concerned. The styling was distinctly Italian, however. There’s also good news for those wishing to have exact replica four into four pipes. They are now available from David Silver Spares. For those who believe the CB350F was slow, as it happens, my 1974 CB350F is the current AMA national speed record holder in the 350cc production classic class and has been since 2014!

1/9/2012 10:47:58 PM

In the mid 70's I had a CB550F with the 4 into 1 exhaust, and custom painted it myself (black with racing stripes). What a smooth running bike! Should have never sold it.

1/6/2012 2:11:53 AM

I bought the first CB350F delivered to Kansas City in 1972 or so I was told at the time. I put about 8K on the clock and by the mid 70's was rearing kids and working my tail off so the bike spent some 35 years parked. In 2007 I gave it away and by 2011 after experiencing a new interest in the little four and decided to get another one. February, 2011 marked the date I added a original condition, well maintained red 72 to my collection and after spending the summer riding it, it holds most favored status right next to my 79 & 80 CBX's and a beautiful green 71 CB750.

bike on highway

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