Yamaha’s first-ever liter-class sport bike, the 1983 XJ900 Seca, was an anomaly for its time.
On one hand the burgundy red bike, with its sleek handlebar fairing, reflected styling trends to come. But many sport bike aficionados contend that the 900 Seca was a motorcycle arriving too late to the party and, coupled with its sketchy performance, never was a contender in the burgeoning heavyweight sport bike market of the mid-1980s.
For starters, the 900 Seca was underpowered for its class. Its inline 4-cylinder engine actually began life in 1980 as a 650 for a smaller model, later evolving to its 853cc displacement in 1983. As it happened, the 853cc engine, although adequate for general road duty, was underpowered compared to its competition.
Moreover, by industry standards the Seca’s suspension package proved obsolete, falling short in its performance compared to other bikes in the budding sport bike category. The Seca’s suspension included an ill-performing air-assist fork with an anti-dive feature up front and twin shock absorbers on the rear; by 1984 mono-shock rear suspension proved to be the accepted norm for any sport bike if it was to be a sales success.
Looking even closer at the Big Picture, three years had elapsed since Suzuki shook the establishment with its dazzling GS1100EX, not necessarily a sport bike, but truly a classic design that helped foster the sport bike genre. The following year, 1981, Honda based its CB900F sportster on the company’s successful CB750F Super Sport platform; by 1983 the CB900F morphed into the CB1100F, and a year later the VF1000 Interceptor helped form Honda’s vanguard of new V-4 sport bikes, originally spearheaded in 1983 by the innovative VF750. Kawasaki? Well, the Big K had a gaggle of GPz models, with the big GPz1100 doing the heavy lifting on Racer Road. And as Honda did with its VF1000 for 1984, Kawasaki secretly had its own ground-breaking model, the Ninja 900, waiting in the wings to trump the field in that same year. And by late 1985 the sport bike world became familiar with Suzuki’s GSX-R1100 (and 750).
Keeping up with the Joneses
Yamaha’s answer to this orgy of cubic displacement overdose was the 900 Seca, a sport bike — of sorts — that traces its roots to the XJ650, a tidy middleweight sport model originally targeting the European market in 1980. We’ll address that “of sorts” comment about the 900 Seca later, but for now we should focus on the XJ650 itself, by 1980 industry standards a rather refined sport bike that relied on an all-new engine to propel it onto the international stage. Yamaha also used a variation of the XJ650’s 653cc engine to power the U.S.-bound XJ650G Maxim that same year. The Maxim was a U.S.-only model developed to pave the way for a new line of cruisers destined to supersede Yamaha’s successful Specials that Americans had been so enamored with since 1978 (in some parts of the country Specials were outselling their standard-based counterparts five to one!).
Now, about that “of sorts” jab. As noted, Yamaha’s XJ650 and Maxim (a word, by the way, that one dictionary defines as “a concise formulation of a fundamental principle or rule of conduct”) shared essentially the same air-cooled inline 4-cylinder 653cc engine, with minor tweaks to tailor their power curves for the bikes’ respective markets. Despite their cumbersome driveshaft with differential final drive layouts, both Yamaha ground-breaking 650s mixed high power with low weight, and in the Maxim’s case gained the distinction as the quickest 650cc-class motorcycle in America at the time; the 1981 Maxim posted a quarter-mile elapsed time of 12.60 seconds (Cycle Guide test) compared to low 13s for most other 650-class players.
In a word, the Maxim engine had moxie. It also was the first inline four to have its AC generator relocated from the end of its crankshaft to a more logical placement behind the cylinders and beneath its bank of Hitachi carburetors (a layout, by the way, already found on Honda’s 6-cylinder CBX). The new arrangement gave the bike additional cornering clearance and a slightly lower center of gravity that enhanced maneuverability when cornering, a bonus, even if the bike was intended more for cruising Main Street U.S.A. rather than strafing apexes on America’s twisty back roads.
The following year the Maxim-based engine, with updated bore and stroke figures, served as the power plant for Yamaha’s new Seca 750 (748cc), a bike that Cycle magazine termed a “bona fide sports bike” (my italics), but not necessarily a bona fide sport bike. The word “sports” gave Cycle editors wiggle room when addressing the Seca 750’s final drive, which included the rather bulky and heavy driveshaft/differential combo — a layout typically shunned for sport bike applications.
Bigger is always better
A slightly reconfigured variation of the spunky air-cooled 653cc engine was also crafted in early 1983 to provide a more durable engine for Yamaha’s new turbocharged entry, the XJ650 Turbo. The turbo engine and drivetrain featured a stronger clutch and reinforced transmission to withstand the more brutal forces that a turbocharged engine might produce. And for the most part Yamaha engineers based the updated 853cc engine variant using the Seca 750’s top end mixed with the clutch and 5-speed transmission from the XJ650 Turbo.
The conversion to the 900 Seca’s 853cc configuration began by stretching displacement from 748cc, following the normal practice of boring and stroking the cylinders and rods. The 2-valve (per cylinder) head received larger valves (36mm intake and 30mm exhaust versus the 750’s 33mm and 28mm valve sizes), plus valve lift and timing were altered accordingly. The Hitachi carbs’ venturi sizes grew three millimeters, from 32 to 35mm, too. As expected, YICA (Yamaha Induction Control System) that used a series of interconnected sub-intake ports to swirl the incoming air/fuel mixture within the combustion chamber for improved burning efficiency was retained. Ignition advance and a higher compression ratio (9.6:1 vs. 9.2:1) all contributed to a claimed 85 horsepower at 9,000rpm, officially lofting Yamaha’s 900 Seca into the liter-class. The 900 Seca was ready for its 1983 curtain call — it was game on.
That, of course, made the 900 Seca free game for the enthusiast motorcycle magazines’ to evaluate and comment, and reading into some of the ride reports, their opinions were mixed, to say the least. For instance, Cycle wrote, “With the Yamaha XJ900 Seca, you get the sport and the shaft, and will be delighted with both.” Cycle Guide was a little less accommodating: “The  Seca is a middle-of-the-pack performer by 750-class standards, that does nothing better than — and some things not as well as — other bikes in its general category [liter class].” Motorcyclist’s editors were even less complimentary about the 900 Seca in their Off The Record comments that, as part of the road test article, were penned by individual staff writers, with one editor going so far as to state that “any of the sporting 750s would leave it [900 Seca] sucking hind teat.” Perhaps Cycle World was the most neutral in its overall assessment about the 900 Seca: “It isn’t as powerful as an 1100, but then it’s not as heavy. It isn’t quicker or faster than the latest 750s, but has a better powerband and turns fewer rpm at cruising speeds.”
In the beginning
Regardless of what the motorcycle magazine mavens wrote, Yamaha forged ahead with its 900 Seca to do battle with the other liter-class sport bikes. The journey revealed some weak points about the bike’s suspension, which Yamaha had fine-tuned specifically for the 900 Seca. For instance, the Kayaba anti-dive fork, originally found on the Seca 750 and updated for the 900, proved rather ineffective on both bikes. The anti-dive feature was more of an anti-working addition, and the air fork legs (with crossover tube to balance pressure in both legs), working in step with adjustable damping, were temperamental in performance; insufficient air pressure (Yamaha specified a range from 5.7 to 17.1psi) resulted in bottoming under heavy braking, while too much air in the fork legs prompted the compression and rebound to react slowly for a harsh ride. Result: depending on road surface conditions, the fork offered either bouncy or choppy behavior.
The rear suspension, composed of two Yamaha-built de Carbon remote reservoir shock absorbers wrapped in dual-rate springs, encountered its own problems and nuances. The two piggyback shocks also offered the rider welcomed adjustability, including four-way adjustable rebound damping and five spring preload positions. The problem, though, was controlling the up and down movement of the rear wheel and its heavy differential at sport-bike speeds. Stiffen the rear springs and corresponding damping rates prompted the rear wheel to, in Motorcyclist’s report, “pop off the ground and break traction” over rough pavement. Cycle Guide and Cycle World experienced similar behavior, while only Cycle’s crew felt comfortable with the Seca’s ride under those conditions.
Despite mixed feedback concerning handling, all editors seemed to welcome the 900 Seca’s neutral steering and generous cornering clearance at full lean while turning. Again, the heavy differential was the final factor in the bike’s handling, especially if the rider, for any reason, chopped the throttle at mid-turn, causing the rear shocks to deeply compress. Likewise, twisting the throttle grip for more power initiated jacking the rear end up. Both behaviors were consequences often associated with shaft-drive motorcycles, and the 900 Seca proved to be no exception.
Another interesting feature played into the 900 Seca’s handling. Yamaha’s new liter bike checked in with adjustable handlebars, a feature whose moment was a long time in coming. Two multi-piece handlebars mounted separately atop the upper triple clamp allowed the rider to loosen and reposition the handgrips within multiple planes to suit just about any angle and height within the rotating range. The two-piece bars were sectioned with corresponding serrated surfaces that provided incremental adjustments. When the most advantageous riding position was achieved the bars were tightened, hopefully creating ergonomics that better suited the rider, all without having to change handlebars! Yamaha claimed 20 adjustment combinations for the handlebars, but magazine editors complained that they were limited to fewer positions due to obstruction by the gas tank, plus the serrated joint edges were large, limiting precise placement with certain positioning of the bars and their hand grips.
Even so, the adjustable handlebars offered a unique and interesting feature. It also played into the hands of the bike’s overall ergonomics that boasted a decent rider’s triangle in relation to foot pegs, handgrips and seat. Overall, the seat’s contour proved acceptable, but most editors deemed its padding was too firm.
The Seca’s biggest fan
The 900 Seca featured here is an all-original survivor, with few exceptions such as the fairing bubble’s fasteners and the Dunlop K505 replacement tires. The bike shows only 6,500 miles on its 39-year-old odometer, and it has a rather interesting history — it spent its years in the hands of three different motorcycle road racers, beginning with one of the all-time greats, Kenny Roberts.
The Seca was part of the inventory at Kenny Roberts Yamaha Country, an authorized dealership in Roberts’ hometown of Modesto, California, so the bike was technically KR’s. The three-time 500cc Grand Prix world champion also had formed a road race team during that same time to compete in AMA Formula 2 (250cc road racing), and one of the team members expressed interest in buying the 900 Seca.
That would be the team’s tuner, Bruce Maus, himself a former racer who had won the AMA Novice (250cc) race aboard his own Yamaha TZ250 at the 1980 Loudon National. With his wife’s backing, he bought the 900 Seca, and it served as their two-up sport touring toy for exploring the scenic backroads of Central California in-between race weekends.
Mrs. Maus also happened to be from England, and during the mid-1990s the couple decided to move back to the Mother Country for a change of pace. Before they left Bruce sought a place to store the Seca and a 1966 Honda CL160 he had bagged at auction. He asked a friend, John Lassak, another well-known mechanic/tuner within the AMA Lightweight ranks, for help. Bruce and John had been friends since their days spent together tuning for MacLean Racing, so they both shared an affection for two-wheel hardware. John accommodated, making space in his storage container where both bikes hibernated for the next 25-plus years (neither John nor Bruce remember exactly when the bikes were parked).
Fortunately, Bruce had the foresight to fill both engines to the brim with oil to keep their innards lubricated, and he doused their exposed bits and pieces with WD40 to prevent oxidation. Unfortunately, at the peak of the COVID lockdown, Bruce had to shut down the Ducati shop that he had established in England. That, coupled with his divorce, prompted him to do a little house cleaning, and among the items to go were the two bikes. He emailed John with a simple message: “Keep the two motorcycles. They’re both yours now.”
On the road again
John really wasn’t in the market for a big bike, but out of respect to his fellow tuner, he rolled the Seca into the garage to commence cleaning and prepping it for its overdue return to road duty. Tuners being the perfectionists that they are, he cleaned and synced the bank of Hitachi carburetors, set the timing, checked the valves, and essentially gave the bike a “pre-race” once-over that included freeing a stuck brake caliper, flushing brake lines, tightening fasteners, etc.
I’ve known John since high school, and he tuned the race bikes for my brother and me during our days in the sport, so Alan and I joined him for some of the finish work, along with mounting the Dunlop 505s with their retro-profile tread contour onto the Seca’s cast wheels. Tending to the older Yamaha reminded us of fun times we shared “back in the day” prepping our race bikes in John’s garage, so naturally we never ran out of things to joke or talk about, recalling old racing episodes and the good times we had.
Best of all, John got the bike running, and we knew that Bruce would be proud if he could have been part of the occasion. Remember, tuners are perfectionists who love to see a good bike get back on the race track, or in this case, on the road again.
Mr. Maus, your motorcycle is ready to ride … again. MC