A 400 on Steroids: Suzuki GS450

Best bets on tomorrow’s classics: 1980-1983 Suzuki GS450.

| March/April 2014

  • 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.
    Image courtesy Suzuki
  • 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.”
    Image courtesy Honda
  • 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.
    Image courtesy Yamaha

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.

earthybike
11/23/2018 3:41:53 PM

I bought an 81 S model recently with low miles and spent a month fixing problems and tweaking performance. There's a screen between the air cleaner element and carbs that was completely clogged and hard as hell to remove and clean but well worth the trouble. I also removed the plastic bushing above the needle in each carb, which cured the warmup issue and helped with low and midrange running. I restricted the stock exhaust at the muffler ends with 3/4" OD EZ-Lock inserts (gotta shim the circumference, though), which eliminated the 4-7k hole to my satisfaction. (Fortunately, the high RPM range was not affected as much as I thought it might). The front forks being soft, I replaced the fork oil with 30 weight. Also added a homemade laminar lip to the cafe fairing, which vastly improved helmet buffeting. An inch-thick seat cover improved the riding geometry, as the seat is too low in my opinion. Finally, a stock luggage rack and a small top case. Once I get some decent handling tires, the bike will be the perfect lightweight daytripper. Thank goodness the previous owners didn't try to cafe this sleeper classic!


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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