Honda CB750 Prototype

Honda CB750 Prototype
Manufacturer	Honda
Production	1968
Class	Standard
Engine	Four stroke, transverse four cylinder, SOHC, 2 valve per cylinder.
Compression ratio	9.0:1
Top Speed	198 km/h / 123.2 mph
Ignition	Battery, coils
Transmission	5 Speed
Frame	Tubular steal duplex cradle
Suspension	Front: Telescopic forks non adjustable. Rear: Swingarm, dual shocks, preload adjustable.
Front Tire	3.25-19
Rear Tire	4.00-18
Wheelbase	1453 mm / 57.2 in.
Seat Height	800 mm / 31.5 in.
Weight	226 kg / 499 lbs (wet)
Oil Capacity	3.3 L / 7 US pints
Recommended Oil	Honda GN4 10W-40
Fuel Capacity	18.2 L / 4.8 US gal
Manuals	Service Manual

It could reach a top speed of 198 km/h / 123.2 mph.

Engine

The engine was a Air cooled cooled Four stroke, transverse four cylinder, SOHC, 2 valve per cylinder.. The engine featured a 9.0:1 compression ratio.

Drive

Power was moderated via the Multi-plate, wet.

Chassis

It came with a 3.25-19 front tire and a 4.00-18 rear tire. The front suspension was a Telescopic forks non adjustable. while the rear was equipped with a Swingarm, dual shocks, preload adjustable.. The CB750 Prototype was fitted with a 18.2 L / 4.8 US gal fuel tank. The wheelbase was 1453 mm / 57.2 in. long.

Photos

Overview

Honda CB 750 Four K Prototype

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.

A turn signal switch unit is beautiful polished aluminum without “TURN” on the unit. On the other hand, K0 has a painted one.

A steering damper on the top bridge gives the meter panel a fresh view. The speedo has up to 150mph on its scale.

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.

A plastic throttle free adjusting nut. K0 has ordinal metal nut.

A brake caliper doesn’t have horizontal 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.

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.

A seat, so called “Red Supo”(?), is the same type on K0.

Make Model	Honda CB 750 Four K Prototype
Year	1968
Engine Type	Four stroke, transverse four cylinder, SOHC, 2 valve per cylinder.
Displacement	736 cc / 44.9 cub in.
Bore X Stroke	61 х 63 mm
Compression	9.0:1
Cooling System	Air cooled
Lubrication	Dry sump
Induction	4 x 28 mm Keihin carbs
Ignition	Battery, coils
Starting	Electric, kick
Max Power	50 kW / 67 hp @ 8000 rpm
Max Torque	44 lb-ft / 60 Nm @ 7000 rpm
Clutch	Multi-plate, wet
Transmission	5 Speed
Final Drive	Chain
Gear Ratios	1st 13.99 / 2nd 9.54 / 3rd 7.45 / 4th 6.14 / 5th 5.26:1
Frame	Tubular steal duplex cradle
Front Suspension	Telescopic forks non adjustable.
Rear Suspension	Swingarm, dual shocks, preload adjustable.
Front Brake	Single 296 mm disc
Rear Brake	179 mm Drum
Front Tire	3.25-19
Rear Tire	4.00-18
Wheelbase	1453 mm / 57.2 in.
Seat Height	800 mm / 31.5 in.
Ground Clearance	160 mm / 6.3 in.
Wet Weight	226 kg / 499 lbs
Fuel Capacity	18.2 L / 4.8 US gal
Oil Capacity	3.3 L / 7 US pints
Consumption Average	6.9 L/100 km / 14.6 km/l / 34.3 US mpg
Braking Distance 48 Km/h / 30 Mph - 0	10 m / 32.9 ft
Braking Distance 97 Km/h / 60 Mph - 0	41 m / 135.7 ft
Standing ¼ Mile	13.5 sec / 100.9 mph
Top Speed	198 km/h / 123.2 mph
Colour	Candy blue/green