Dunstall 750 Triumph
DUNSTALL 750 TRIUMPH
CYCLE WORLD ROAD TEST
It's a Pseudo-Racer For Serious Play, But Treat the Brake Lever With Care. and Watch Out for the Law.
THERE IS A BREED of motorcyclist endemic to England but increasingly common in the U.S.—the cafe racer. The English cafe racer/enthusiast is a sight to behold. Rather than the lazy ape-hangers and sissy bars of supine highway cruising, his bike sports clip-ons, rear set pegs, and road racing tank and seat suited for prone navigation of the cobblestone. Though uncomfortable, that’s where it’s at in England and that’s why Dunstall can sell something like the 750 Triumph with street equipment.
The Dunstall Triumph is a high-mettled racer/tourer in its own right and is made for experienced and disciplined guidance. It is a serious machine capable of genuine ferocity. Not given to merriment, but to hard challenge, it will slip through the wind at better than 120 mph and rage over the landscape with choleric haste.
It is not the machine for one of marginal experience and more than emotional abandon is needed to ride it well. There’s more to racing the Dunstall than sitting astride it and working the levers. This bike is no fun at all under 80 mph unless you like being stared at by the curious. It plainly does not lend itself to about-town ego-feeding cruises and is quite unhappy under 30 mph even in low gear. But if you have lots of room or access to a road race course, the Dunstall is a sheer gas. It also is a hot rod, so one can be a bit more forgiving of the weird noises, oil puking and smoking-things that would be strongly criticized on a more standard production bike. We should mention that these disturbances occurred, however, and the prospective buyer in America would do well to come prepared with Locite, extra screws and wire—and be a halfway competent mechanic.
The Dunstall’s handling is excellent. At high and low speeds it behaves exactly the way a bike should; we couldn’t ask for more. The 750 is one of the best handling motorcycles ever tested by the CYCLE WORLD staff. This fact is rather amazing because the frame, front forks and rear Girling spring/clampers are T 120 units, a definite tribute to the innately good handling characteristics of a production Triumph. It also demonstrates how much you can improve the handling of any bike by installing clip-ons, moving the foot pegs rearward, and using road racing style tires-especially a ribbed front tread, rather than the usual K-70, which allows the rider to hold a truer line when the bike is leaned over hard. This is particularly evident on the Dunstall, as it can be cranked over so truly to the precise angle of lean that at racing speeds it doesn’t feel heavy at all when pushed through a turn—and this is a machine of substantial dimensions. Its ground clearance is generous, thanks to the Dunstall pipes and mufflers, and the bike must be hung out at a precarious angle before things begin to scrub away. The centerstand is vulnerable during low leaning lefts, however. In spite of this, and regardless of the bike’s attitude or speed, the rider enjoys a sensation of supreme confidence that comes from its unerring stability. In this respect, the Dunstall is, strangely, a most relaxing ride indeed.
The brilliant red head fairing is of an excellent design, and is an ideal compromise for the rider who doesn’t want to encumber his machine with a full fairing. Also, a full fairing reflects engine noise upward and would take a merciless toll in day-in-day-out riding by way of rider fatigue. In event of an accident a full fairing may be damaged more easily, too. The 10-oz. grade fiberglass is not of the best quality and showed signs of vibration cracking, even away from mounting areas. It is thin, fabricated over the gel coat with a chopper gun, rather than being layed up on webbing. Web construction would be stronger, and resist vibration better when thin glass is used. Nonetheless, it is a valuable asset for high speed riding.
The braking abilities of the Dunstall Triumph must be experienced to be believed. While the rear brake is a stock Triumph unit, the front brake is a Lyster hydraulically operated twin-disc affair. The machine hauls down from 120 mph in a fantastically short distance. There is absolutely no fade, and therefore no fear of overshooting a fast turn, even when braking is delayed until the last millisecond. From lap to lap, the rider will not have to move his shut-off point backward from the turn to compensate for brake fade.
However, hydraulic operation, coupled with such brutal stopping power, poses a great danger for the uninitiated. Travel at the handle from “off” to wheel-locking tension is very short. There is no progressive feeling at all. This would make the brake extremely treacherous in the wet or similarly marginal traction conditions. There is no “feedback’' from the braking surface through mechanical linkages to the lever, as there would be on a non-hydraulic brake. In other words, this brake is for the expert rider.
Cold starting the Dunstall was remarkably easy; just open the fuel taps, tickle the concentrics, and one easy heave usually would light it. Unless the weather is cooler than 50-60 degrees the choke isn’t needed. Warm starting takes more effort as it tends to flood more easily. About that choke. It is often necessary to wire these things open, as they are likely to vibrate to a partially shut position. A 15-minute ride will cause the lever to creep around sufficiently to inhibit performance and, naturally, gas mileage.
The Lucas electrical system worked flawlessly throughout the test. Spark is supplied to the NGK plugs by a Lucas capacitor ignition. Engine speeds reached 7500 rpm during the test without the slightest sign of incontinence from the unit. The horn, however, is something less than authoritative and it’s highly unlikely that even the humblest of Detroit iron will cringe at its pusillanimous yelp. The ammeter is mounted in an instrument panel in the fairing, along with the speedometer and tachometer. The latter two dials are quite easy to read at speed and relatively immune to vibration of the fairing. Such is not the case with the ammeter, as its needle oscillates through almost every degree of its spectrum when the bike is underway. This, by the way, is not in the least unusual on machines equipped with ammeters. However, they are roughly indicative of charge or discharge rates when the bike is not moving.
A Dunstall Triumph carries relatively tall gearing, e.g. 103 mph in third. This is because Dunstall gears for the torque peak rather than peak horsepower. Besides yielding respectable gas mileage (40 mpg at 65 mph), high gearing allows high speed cruising at moderate engine revs. The bike’s torque is very strong above 70 mph and will pull the machine up past “the ton” in a remarkably short time with nary a change in exhaust note. The gears are stock Bonneville touring ratios with the only changes being in final drive ratio and tire size. Riding easily, first gear starts require substantial clutch feathering. The gap between second and third gears is quite noticeable, although not bothersome. The machine would be clearly capable of 105-107 mph quarter-miles and low 12-sec. e.t.s were it geared for acceleration rather than road racing. The highest quarter-mile times were obtained using third gear through the trap, and the best e.t. was obtained by revving to peak torque and breaking the tire loose at the start. Shifting was done at 7200 rpm except for the second-to-third change which took place at 7400 rpm.
The increase from 649 to 744 cc is obtained by fitting the Dun stall aluminum barrel conversion to stock Triumph crankcases. The bore is enlarged from 71 to 76 mm while stroke remains unchanged at 82 mm. The cylinder head has been modified by way of enlarged, reshaped and polished ports. Bronze, Hi-Dural valve guides have been fitted along with special progressively wound valve springs, and the stock pistons have been exchanged for units which deliver a 10:1 compression ratio.
The cams are the stock grind used on the Bonneville and TR-6. The bike’s somewhat cammy response is due to the headwork and raised compression. All in all, the engine’s state of tune is far from inflexible, although lope is evident at idle. And while not in a perfect mechanical state, the Dunstall ran extremely strong when fully wound out to 7400 rpm. Because of this, the performance figures can be considered fairly representative.
With the fairing, alloy wheels, 4-gal. fiberglass fuel tank, clip-ons, and disc brake, a simple hot rod Triumph has assumed a mystic and fierce identity. It is surely less than an all-out racing bike but much more so than other street tourers. Its appearance is so exalting, even the most apathetic personality would blink as it passes. [O]
DUNSTALL
750 TRIUMPH
$1400
SPECIFICATIONS
TEST CONDITIONS
PERFORMANCE
