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Honda CB 750 Custom       

 

 

 

 

Make Model

Honda CB 750 Custom

Year

1980

Engine

Air cooled, four stroke, transverse four cylinder, DOHC

Capacity

748
Bore x Stroke 62 x 62 mm
Compression Ratio 9.1:1

Induction

4x 30mm Keihin carbs.

Ignition  /  Starting

CDI  /  electric

Max Power

72 hp @ 9000 rpm

Max Torque

67 Nm @ 7000 rpm

Transmission  /  Drive

5 Speed  /  chain

Front Suspension

Adjustable telehydraulic fork. 

Rear Suspension

Swinging arm fork with adjustable shocks absorbers

Front Brakes

2x 276mm discs 1 piston calipers

Rear Brakes

190mm Drum

Front Tyre

110/90-19

Rear Tyre

130/90-16

Dry-Weight

252 kg

Fuel Capacity 

16.2 liters

Consumption  average

42.9 mp/g

Standing ¼ Mile  

12.7 sec / 166.1 km/h

Top Speed

204.7 km/h

AT A TIME WHEN SOME SPECIAL-TYPE motorcycles seem little more than clay mock-ups, Honda has given us a genuine working model, capable of being ridden not only to the local hang-out, but to points beyond. Specials, as sometimes put into practice, can air-out their problems on riders within 45 minutes in the saddle. After spending some time on the CB750C, you will come away feeling that Honda's engineering people tried to make working metal out of molded clay, and did.

The 750, Honda's biggest street seller, has been with us in one form or another for over 10 years. Honda considers the Custom their standard model; in the 1980 model-year it outsold the F- and K-mod-els combined two-to-one. While each model has its own look, in basic hardware all of Honda's current 750s are very similar. All of them employ the same frame, with slight differences in front-end geometry and rear-shock length and type, and these subtle mechanical variations make the motorcycles different in important ways.

In the 1981 model-year the swing arms of all 750 Hondas ride in needle bearings where the arms attach to the dual-down-tube frames. Needle-bearing arrangements, along with having a better service life than bushings when the needles are properly sealed and protected, can add to chassis rigidity, and in turn complement the handling of the motorcycle.

In this new model-year the Custom gets an air-assisted fork very similar to the new unit used on the CB900C (Cycle, September 1980). Unlike last year's fork, this one is a leading-axle affair. The 35mm fork tubes are carried in new triple clamps that have spread the fork-tube spacing from 182mm to 192mm. According to our Honda sources, numerous tests comparing the leading-axle and center-axle forks showed that a straight swap to a leading-axle fork increased slider stiction as much as 20 per cent. To counteract this, Honda pulled the tubes back with the new triple clamps, giving it five millimeters less trail and making the fork-tube angle two degrees and 45 minutes steeper, thus compensating for the placement of the axle on the leading edge of the fork slider. After these changes, Honda found no increase in stiction. Chalk up one to engineering, and one to styling.

The new fork has Syntallic bushings. These are attached in the fork assembly at two places: the top of the slider and the bottom of the fork tube. "Syntallic" is a synthetic Teflon-type material, which is tough enough for heavy loads yet provides a very slippery surface for the tube and slider bearing areas.

Fork oil is a vital component of smooth fork operation, and with the change to a leading-axle fork, oil capacity has increased from 175cc to 245cc, an added volume of 70cc per leg.

Also new to the front end this year are dual-disc brakes, a much-appreciated addition. The 1980 K-model tested last year (Cycle, September 1979) was greatly in need of a stronger front brake. Now, when repeated high-speed stopping becomes necessary, you will be able to do so without having the brake lever come back to the handlebar. Our only complaint concerns the spongy feel at the front brake lever. When the lever reaches the serious engagement point of the front brake, it mushes back too close to the handlebar, making precise braking and throttle control difficult.

This year's VHD (Variable Hydraulic Damping) shocks are a slight rework of last year's FVQ shocks. They have the same ball-and-spring-controlled variable rebound damping, but with improved construction tolerances and materials. The shock shaft has been plated with a harder, more durable chrome to forestall any possible leaks caused by pitting or scoring of the shaft surface.

Honda has upgraded the springs, which according to Honda aren't as susceptible to sagging. Unfortunately these springs are so stiff that the ride gets uncomfortable. This shortcoming results from building the motorcycle to "Cruiser" specs. The rear shocks are over-sprung for one apparent reason: to solve the ground clearance problem that would result from a low seat height, which was produced, in turn, by fitting shorter shocks. The shocks are one full inch shorter than those on the F-model. It's a trade-off. The low seat is a very appealing item; it makes moving the bike around while astride much easier, and it also makes the bike easier for the rider to stabilize while taking on a passenger. The lower ride height and reduced suspension travel make the stiff springs an unwelcome but necessary addition, and one which trades off comfort.

Electrically the Honda is the same as last year, save for the new quartz-halogen headlamp—a seven-inch Stanley with an H4 bulb. You might balk at the $13.45 price of a replacement bulb (the bulb is changed; you retain the housing/ lens) until you have a chance to ride the bike at night. Once you do, you would gladly pay twice the price for the bulb, just for the increased light. The beam has an excellent spread on both low and high beam. The peripheral pattern of the light is organized so that, when the bike is being cornered, the outer part of the beam tilts upward on the horizon, allowing you to see far into the distance.

This year's engine specifications remain the same as last year's. In fact, the Custom's engine is identical to the F-model's, except for the exhaust system and carburetor jetting. The C-model has less power, thanks to its stylishly short exhaust system. The F-type simply breathes better, having bulkier and more efficient exhaust plumbing.

Another feature added for 1981 is a small vacuum-operated fuel valve. This convenience item shuts the gas off when the engine isn't running, thus eliminating the chance that there might be a pool of gas spreading across your garage floor, searching for the water heater. Convenience and safety.

The seat, redesigned this year, has been lengthened to allow the pilot to sit farther back. This might have benefited the rider had the bike had a standard seat/footpeg/handlebar arrangement, but in this particular case we could find no apparent advantage.

Riding with feet on the passenger pegs seemed more natural to our test riders than using the far-forward-mounted rider's footpegs. Putting their feet on the forward pegs would bend our test riders' torsos in such a way that old devil lower-back-pain would make a visit. Obviously shorter staffers suffered more than the six-foot crowd; but no matter the length of our test inseams, two hours on a straight road wasn't pleasant at all. Kicked-back might be great for around-town short-time prowling, but for that Long, Lonesome Highway the Custom just doesn't make it.

New paint graces the 4.4-gallpn fuel tank. The Custom delivered a 42.9 mpg average, allowing 3.7 gallons and 158 miles before the switch to reserve. Once there, the remaining 0.7 gallon will take you about 30 miles before you get to try out your new jogging shoes.

This Honda C-model puts out a fair amount of engine vibration, which the long handlebar tends to amplify enough to blur the mirrors at anything above 58 miles per hour. The footpegs vibrate also, but that is more of an observation than a complaint. Moreover, about the time our bike passed the 1000-mile mark, vibration seemed less pronounced.

Spend much time in the mountains with the CB750C and it will let you know where it would rather be: on the boulevard. The motorcycle handles fairly well, but its Custom-related limitations become as evident as a lighted billboard at midnight. The plush ride the fork gives on the boulevard becomes terribly under-damped in the hills. There, the fork pumps up and down through its 6.25 inches of travel with seemingly wild abandon. In cornering, all of this fork movement translates into constant steering changes, which in a fraction of a second can lead to a wobble that stays until you slow down, stop turning, or both.

The fork, with its lack of stiction, is outstanding. The sliders are a blur of activity on any semi-rough surface. If Honda can find a way to adequately damp the fork for spirited riding and still retain its remarkable freedom from stiction, the company will have a winner. For now, though, the fork remains under-damped when the pavement begins to dart left and right.

Then there are the rear shocks. The stiff rear springs give the bike a harsh ride. If you set the preload down so the bike has a somewhat softer ride, what little cornering clearance you had becomes history. It's a shame that the generous compliance and travel of the 1981 fork must be compromised in the rear by travel and springing reminiscent of 1971. Rebound damping was fine, but the compression damping was lacking for the amount of travel and ground clearance available. If Honda were to soften the springing somewhat and increase the compression damping, they might accomplish the same thing they did with the stiff springing but give the bike a more compliant freeway ride.

The Honda exhibits neutral steering; a slight touch on the handlebar has it go where you would like. At medium speeds it is quite nice, excepting the suspension components' unsettling behavior. At low speeds, the Custom is a little cumbersome, not quite settling into the arc or lean angle that you had intended. But as a whole, for the market for which it is intended, the Custom's steering is entirely adequate.

If you intend to pull away from a stop and turn left and have your left foot on the ground to steady the bike, you'd better watch out. More than once we left a supporting toot on the ground a fraction of a second too late and got it wedged under the centerstand tang as we pulled away from a stop. Those who value their Achilles' tendon will keep their feet clear of the left side of the bike.

Cold starting was something we never had a chance to evaluate. During the time we tested the Honda, ambient temperature never fell below 65 degrees. Car-buretion was quite good, except for a lean spot that showed when cruising at a steady 55 mph. The bike needs a large amount of throttle twisting to maintain speed uphill, caused we think by the accelerator-pump lag time. When the pump finally kicks in you find yourself rolling back the throttle to compensate for the extra speed this generates. Perhaps recalibrating the pump would cure this .

The clutch has a nice, light pull. Its somewhat narrow engagement point can combine with the light flywheel effect of the engine to produce an occasional stoplight stall. The clutch is a strong one, though; no abuse we gave it made it slip.

Our test bike had a fourth-gear problem. We had to be very careful when shifting into fourth, going up or down. From time to time when shifting from third to fourth, the lever would feel as though it had engaged fourth, when in fact it had left the transmission in third gear. Other times we would find false neutrals, whether shifting up or down. We thought this might be singular to our test bike, but our 1980 K-model had exhibited a similar fourth-gear touchiness, though the 1980 CB750F tested in April 1980 had no glitch in fourth gear. Our Custom would produce fourth, providing care and time was taken getting it.

The CB750C fits into the Custom arena filling a space that has needed filling for sometime. It's more of a centrist motorcycle, being less extreme than its stylized brethren. Although it still has the look of the Custom, its riding position isn't quite as uncomfortable and compromised as others, some of which have you sitting with your wrists in your chest.

The Honda has faults, but it is a successful attempt to make a better motorcycle out of the Custom theme, and for that Honda should be applauded. €>

Source Cycle Magazine 1980

 

 

 

NOTE: Any correction or more information on these motorcycles will kindly be appreciated, Some country's motorcycle specifications can be different to motorcyclespecs.co.za. Confirm with your motorcycle dealer before ordering any parts or spares. Any objections to articles or photos placed on motorcyclespecs.co.za will be removed upon request.  

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