A 400 on Steroids: Suzuki GS450

Best bets on tomorrow’s classics: 1980-1983 Suzuki GS450.
By Motorcycle Classics staff
March/April 2014
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In Japan, 400cc bikes are popular because they classify as “medium” size; go bigger than 400cc and you’re in a more expensive tax class. But that line in the sand doesn’t apply in the U.S., so Suzuki gave its little twin a cc boost to make it more appealing to U.S. buyers. The Suzuki GS450 was really a 400 on steroids. Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up.
Photo by MC Staff
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Suzuki GS450ET/ST
Claimed power:
38hp @ 9,500rpm (measured at the rear wheel)
Top Speed: 100mph
Engine: 448cc air-cooled, DOHC parallel twin
Weight (dry): 386lb
Fuel capacity/MPG: 55-50mpg
Price then/now: $1,739 (ST), $1,659 (ET)/$700-$1,500

The Suzuki GS450 was really a 400 on steroids. In Japan, 400cc bikes are popular because they classify as “medium” size; go bigger than 400cc and you’re in a more expensive tax class. But that line in the sand doesn’t apply in the U.S., so Suzuki gave its little twin a cc boost to make it more appealing to U.S. buyers.

Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up. The 180-degree crankshaft was now one piece (it was built-up on the 400 and 425), and ran on three automotive-style plain bearings instead of balls and rollers as before. The bore was stretched from 67mm to 71mm, while stroke was shortened from 60mm to 56.6mm.

Beyond that, the GS450 engine was just like earlier versions. A single self-adjusting chain spun two overhead camshafts, which in turn operated two valves per cylinder, with a 36mm intake and 30mm exhaust. A revised gear-driven engine counter-balancer quelled primary vibration and rocking forces, and helical primary gears drove a wet multiplate clutch and 6-speed gearbox with chain final drive. Two 34mm constant velocity Mikuni carbs fed the combustion chambers, fired by transistorized electronic ignition.

The drivetrain slotted into a dual-downtube steel tube cradle frame with hydraulic front forks and swingarm rear suspension with preload adjustable shocks. A single-disc front brake and rear drum provided stopping. The package was available as the naked GS450ET or the sportier GS450ST with a handlebar-mounted quarter fairing; Suzuki called the GS450ST their “little café” in period ads. A cruiser-style GS450L rounded out the 450 lineup.

The GS450 was well-equipped, too. Starting was electric only (earlier 400s and 425s had a kickstart lever, as well), the battery fed by a 3-phase alternator. The steering lock was built into the ignition switch, and a storage bin was hidden in the tail section behind the locking seat; a helmet lock was also included. In a period review, Cycle magazine’s only equipment beef was that the turn signals were not self-canceling.

The result was a lively performing bike in a lightweight but sophisticated package. On the strip, the GS450 ran the quarter in 14.1 seconds at 93mph, topping out at around 100mph, and it could stop from 30mph in 32 feet. And with fuel consumption in the 55-60mpg range, the GS450 suited the tough economy of the early 1980s.

Unfortunately, the bike’s EPA mandated fuel stinginess had a penalty: The GS450 ran noticeably lean, and every single period review damned the model for its poor carburetion. Cycle noted “an extended warm-up period” before their test bike would run without the choke. And even at operating temperature, the engine would easily stall when pulling away from a stop, suffering from “a deep hole just off idle,” Cycle said. Throttle transitions were jerky, with the engine hunting when running on a flat throttle, and this was not helped by excessive drive-line lash. Cycle Guide’s Paul Dean said this ultimately led to “aggravation and blind rage” every time he had to roll on or off the throttle out on the open road, adding that “every on-off-on transition of the throttle is answered with a sudden whiplash-quality lurch.”

Cycle magazine liked the sporty riding position and slice gearshift (in spite of a remote linkage), but also found the front suspension to be under-clamped, leading to “pogo-sticking” on rough surfaces: “A series of bumps caused the entire bike to bounce on its suspension, radically affecting ground clearance and steering stability,” the magazine said. Cycle’s testers improved front end performance by upping the fork oil weight from SAE 5-10 blend to straight 30-weight.

Aside from the frustrations of driveline lash, lean running and limp suspension — the last two can be easily fixed now, the former by removing shims above the slide needles for a fatter fuel mixture, the latter with up-rated suspension bits — testers found the GS450 pleasant enough. “The Suzuki excels in terms of the little comforts as well as in the major categories,” Cycle wrote, “… it offers more performance and detailing bonuses than any of its rivals.”

As neat a package as the naked and café variants of the GS450 presented, their cruiser-styled offspring appear to have captured a larger market. Suzuki dropped the sporty GS450s after 1983, but kept the cruisers — and an automatic version — in its U.S. lineup through 1985.

Contenders: Parallel twin rivals to Suzuki’s GS450

1980-1981 Honda CB400T Hawk
Claimed power:
34hp @ 9,000rpm
Top speed: 100mph
Engine: 395cc air-cooled SOHC parallel twin
Weight (dry): 391lb
Fuel Capacity/MPG: 50-55mpg
Price then/now: $1,798/$800-$1500

Honda had a head start in the 4-stroke sub-500cc class, replacing its aging CB360 in 1977 with an all-new 400cc OHC 180-degree parallel twin boasting three valves in each “pentroof” cylinder head chamber. Restyled for 1980, the CB400 gained an extra gear to make six, lost its kickstarter and replaced 32mm Keihins with 30mm versions — though now with an accelerator pump to fix jerky throttle transitions. The pressed steel backbone chassis used the engine as a stressed member and ran on Honda’s composite ComStar wheels sprung by a conventional front fork and dual rear shocks. Front brake was disc, with a drum rear.

Honda tuned the CB400 engine for midrange torque, courtesy of its “power chamber” exhaust collector box, but it still turned in a respectable 14.3-second quarter-mile run at 91mph. And on the road, Cycle magazine found it to be “one of the best handling motorcycles available today,” with “light, precise and responsive steering.” Cycle’s gripes were limited to noticeable driveline lash, a fade-prone front brake, vibration at high revs and cheap, stiction-prone fork seals. They also noted a few missing conveniences, including the lack of an integrated steering lock and no self-canceling turn signals.

Summing up its impressions, Cycle Guide called the CB400T “a bike that answers your commands instantly and zings around corners with speed that will be the envy of 750cc riders.”

1982-1983 Yamaha XS400RJ Seca
Claimed power: 34hp @ 10,000rpm
Top speed: 100mph
Engine: 399cc air-cooled DOHC parallel twin
Weight (dry): 372lb
Fule Capacity/MPG: 55-65mpg
Price then/now: $1,999/$800-$1,600

At first pass, the Yamaha Seca 400’s spec sheet reads a lot like the GS450: an air-cooled, double overhead cam, 2-valve, 180-degree parallel twin with counterbalance shaft, 34mm Mikuni CV carbs, transistor ignition, gear primary, six speeds, 14.1-second standing quarter at 92mph, braking from 30mph in 32 feet and a 100mph top speed.

Principal differences were the box-section spine frame, mono-shock rear suspension, cast wheels, manual cam chain adjustment (versus automatic), self-canceling turn signals, separate jack shaft for the alternator — and the Seca’s party-piece, Yamaha Induction Control System (YICS), designed to promote swirl for better combustion for increased power at low revs.

However, compared to the GS450, the Seca did things in a much different way. To compensate for its relative shortage of cubes the Seca’s torque output peaked at 8,000rpm and power peaked at the bike’s 10,000rpm redline. Despite the YICS, “...we rarely let the Seca’s engine speed drop below 5,000rpm, because there’s nothing there,” Cycle World said. Yet they liked the Seca’s long fuel range and 60mpg-plus economy, its comfortable seat and riding position, and found the suspension to be “as good as — maybe better than — anything else in its class.” In terms of handling, “The Seca changes direction easily and is easy to ride quickly,” Cycle said, concluding, “...the Seca is a serious, competent motorcycle worthy of any rider’s attention.” MC


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Southerner
5/29/2014 9:52:47 PM
Had one. 60 MPG was most definitely true. Didn't have the throttle issues but it did take a long time to warm up. Lovely little bike. I had the cafe model, complete with very functional bar-end mirrors standard. Not sure I ever made it to the ton. The "bin" in the tail was barely big enough to hold summer gloves but still handy for small stuff. If you want to turn off the headlights, unscrew the plastic slider off, trim off the additional plastic that blocks the slot and screw it back on. All they did to keep the lights on was make a slight change to one plastic molding.








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