Honda Cb750f
HONDA CB750F
Long-Term Report
When Honda introduced the twincam 750 in 1979, the new machine was a rebirth for Honda's traditional sports bike, a good excuse to use the cylinder head first seen on the factory endurance racers and a shrewd move in the sales department.
The new 750 was also a good bike. In the F (sports), K (four-pipe traditional) and C (for Custom) variations, the 750 sold well and the 750F won its class in CWs annual Ten Best competition for 1979 and 1980. A sporting mount, we said at the time, while being suited for long trips and for daily use.
The F was thus a good candidate for a long-term test; 10,000 miles or one year, whichever came first. We got a spanking new 1980 750 in the spring of 1980.
Twelve months and 11,000 mi. later, the test was concluded. In terms of drama and trauma, nothing much happened during the test period, which is about the nicest thing one can say about a motorcycle in daily use.
Service Record
Because we were doing some carburetor and exhaust experiments at the time, we ran the 750 through some of our test procedures with 3,000 mi. on the odo. These baseline runs showed our bike to be just a bit slower than our 1980 test 750F, with quarter-mile figures of 12.88 sec. at 99 mph vs 12.54 sec. at 106 mph. The longterm runs were on a warmer day, but still, our bike was not one of the best from the 1980 production run.
Nor did it give any trouble of note. The first pages of the log show nothing except oil changes at the prescribed intervals. The 750 in daily service gave miles-pergallon in the high 40s to low 50s, which matched what our test machine returned.
The only criticism in the record concerned the battery, or more precisely the concealment of the battery. Checking the fluid level requires removing both side covers, undoing both terminals, unbolting the door of the battery box and wrestling the complete unit out. That’s more effort than simple maintenance should take so it’s faint praise to say the battery didn’t need water often and that the battery held up through the year despite not getting checked as often as the book calls for.
The exhaust and carb experiments cooked the original clutch, which was fixed by replacing all the plates. That doesn’t exactly count as an in-service flaw, though, because repeated dragstrip use isn’t what the bike is intended for. On the other hand, the 750F is supposed to be a performance machine and other sports bikes for instance Kawasakis, have come through similar programs unscathed.
(As a side note, our testing involved building and buying exhaust systems, and juggling carb jets, to see if we could get measurable improvements with no penalty in noise or loss of ground clearance, serviceability, etc. In brief, the pipes either didn’t deliver much gain in power or they were so loud, 94 decibels and up, that the socially concerned on staff refused to ride the bike.
The carbs got larger main jets, which did help with the pipes but which introduced blubbering at part throttle, and raised needles, done with small washers, which made the mixture too rich off idle. The 750 can be modified for more power, but because our minor changes weren’t getting anywhere without more trouble than they were worth, we returned everything to stock.)
Since the engine had been unmercifully thrashed, at 5200 mi. the bike went to our local dealer for an inspection of valve clearances. The four-valve Honda head uses shims, but the factory has issued a tool which compresses the valve springs and allows shim replacement with the camshafts in place, so the check was done for one hour of working time and $25.
The 750’s only full service came at 6838 miles, when it went to the dealership for a full tune-up, with filter, valve adjustment, plugs and a compression check, more for curiosity than anything else.
The valves needed shims here and there and the compression test showed 170, 170, 175 and 175 psi for cylinders one through four, well within the specs for the engine. No problems, in short. Mpg all this time was still averaging in the low 50s, with 200 mi. the usual range until the tank needed to go on reserve. Fill-ups were between 3.6 and 3.9 gal.
Products Tested
Because each long-term bike is assigned to somebody on the staff, and because each rider has personal preferences, no motorcycle in the shop stays stock for long. The 750F got a set of lower bars, formerly mounted on a KZ550, almost immediately.
The bars themselves suited our man fine, but they did show that Honda’s use of weighed bars tuned to dampen the engine’s vibrations, works. The different bars delivered a more sporting posture, a more comfortable seating position and a tiny buzz at the grips that gave a numb right hand after an hour or two unless the rider made an effort to relax his grip or shift his fingers.
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The 750 was also used for the Cyberlite (CW, Sept., 1980) pulsing brake light that’s been proved, in a taxi fleet at least, to reduce the chances of being bashed from behind. Our test was negative, in that the 750 was rammed once before the installation and didn’t get hit afterwards.
The Shoei FM-2 fairing (CW, Feb. ’81) was an unqualified success. It’s light, went on with no hassle and deflected headwinds while not adding more than a pound or two. Pity the silver model was out of stock, because color matching would have made the slick 750F even slicker, but black worked anyway. At $129.95, it’s a good deal.
The E-Z Berg seat (CW, April, ’81 ) was custom padded, for the 750 and for the man who rode it most of the time. The purist element objected to a touring saddle on a sports bike and riders who were different heights and weights didn’t fit as well as did the man for whom the seat was made. Still, he thought it was great and the cover and stitching are still intact and watertight nearly a year after the installation.
The Hannigan STe fairing (CW, April, ’81) is a frame mount, with lowers, and added nearly 30 lb. to the front of the bike. It had to come all the way from eastern Canada, it was nicely color matched, right down to the trim stripes, and at $710 complete it wasn’t cheap. It gave the 750 a GP look and kept our man warm and nearly dry all winter long. We and the bike’s new owner were so pleased with the project that he bought the fairing as well as the machine. Nobody wanted to break up a good combination.
The original equipment tires, Bridgestone Mag Mopus, were adequate but were removed at 3400 mi. so we could try Goodyear’s tubeless HSTs.
Part of the experiment was a disaster, due entirely to our mistake. There was a choice of two HSTs for the front; a wavepattern MM90-19, or a ribbed MJ90-19. They are the equivalents of a 3.75 and 3.25-19. On the belief that if some is good, more is better we first installed the bigger front tire.
Wrong. There was no gain in traction or in comfort or control. All the fat tire did was make the steering vague and heavy.
With ribbed MJ front and wave MP90-18 rear the HSTs were fine. They stick until the pegs scrape, they gave good grip in the rain and under braking. After 8000 mi. rear tread has gone from 0.275 in. to 0.075 in., which is to say just about done. Part of the use was at the drag strip, so we’d project a tread life of 8-10,000 mi. in moderate service. Front tread went from 0.185 in. to 0.125 in., roughly onethird the wear so the front tire should be good for at least 20,000 mi.
A pair of Koni shocks, model 76P-1296 with progressive (100/140/173 lb./in.) springs went on after the Hannigan fairing. This may have been a mistake, because the added weight on the front wheel made the 750F more touring and less sports. No real loss, except that it meant the bike didn’t spend as much time being pitched into turns and across bumps, so the Konis didn’t get tested for their full range. They improved the ride and were less liable to being bottomed than were the stock shocks, but that’s as much as we can fairly say.
Other notes: Throughout the test period the 750F missed an occasional shift when not prodded firmly, a common Honda problem. The front brake pulsing lessened with age. We never did find a fuel the engine really likes; on leaded premium, nolead premium and even leaded with octane booster, rolling on the power at less than 3000 rpm always resulted in a ping. The o-ring chain was adjusted only when the rear tire was changed and went the rest of the time without noticeable wear.
All in all, an eminently satisfactory motorcycle. It lived up to its promise and did its job. As they say in the tests, we were sorry to see it go.
