Power Trip: 1985 Suzuki GS1150ES

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1985 Suzuki GS1150ES
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1985 Suzuki GS1150ES
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1985 Suzuki GS1150ES
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1985 Suzuki GS1150ES
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Jose Rumbaut shows us another angle of his GS.
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1985 Suzuki GS1150ES
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1985 Suzuki GS1150ES
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Despite having covered more than 30,000 miles, Jose’s GS looks like new.
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Despite having covered more than 30,000 miles, Jose’s GS looks like new.
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Hidden behind the side fairings, the 1,135cc air-cooled inline 4-cylinder puts down 100 horsepower at 8,500rpm.
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1985 Suzuki GS1150ES

1985 Suzuki GS1150ES

  • Engine: 1,135cc air-cooled DOHC inline 4-cylinder, 74mm x 66mm bore and stroke, 9.7:1 compression ratio, 100.44hp @ 8,500rpm (period test)
  • Top speed: 141mph (period test/half-mile run)
  • Carburetion: Four 36mm Mikuni BS36SS
  • Transmission: 5-speed, chain final drive
  • Electrics: 12v, electronic ignition
  • Frame/wheelbase: Dual downtube cradle, round and box-section mild steel/61in (1,550mm)
  • Suspension: Air/oil telescopic fork front, Suzuki single-shock Full Floater aluminum box-type swingarm rear
  • Brakes: Dual 10.8in (274mm) disc front, single 10.8in (274mm) disc rear
  • Tires: 110/90 x 16in front, 140/80 x 17in rear
  • Weight (w/half tank fuel): 557lb (253kg)
  • Seat height: 30.8in (782mm)
  • Fuel capacity/MPG: 5.3gal (20.5ltr)/49mpg (period test)
  • Price then/now: $4,785/$4,000-$6,000

When Suzuki launched the GS1150ES in 1984, a single word succinctly summarized the machine — horsepower. There were 100 ponies chomping at the bit in the engine department, and Cycle World magazine pushed its test bike through the quarter-mile in 10.94 seconds.

That, said Cycle World in its April 1984 review, made the GS1150ES the quickest production bike the magazine had ever tested. Motorcyclist made similar statements. In fact, that magazine clocked the bike at 10.47 seconds in the quarter-mile.


Such prodigious locomotion wasn’t lost on self-described two-wheeled street hooligan and adrenaline junkie Jose Rumbaut. He grew up in Chicago, Illinois, racing BMX bicycles, but as a young teen he longed for a two-wheeler with an engine to go faster. Luckily, his father, Jose Sr., owned motorcycles as a young man and was sympathetic to his son’s dreams. His mother, Raquel? She just didn’t want him to get hurt.

“I started off on a minibike in the eighth grade,” Jose remembers. “I think it was a called a Fat Cat; it had a huge rear tire and the engine had tons of power. From that point forward, I always had a connection to motorized two-wheelers.”

When he was old enough to ride on the street, Jose and his father bought a used 1978 Kawasaki KZ400. Capable with his hands, a skill Jose picked up from his father, he went through the KZ and soon became known among his friends for his tuning skills. Those talents were put to good use when he also took up dirt biking, riding hard on the trails and then fixing what broke. “I enjoyed riding on the street and in the dirt, but I also loved racing on the street and on the track and doing wheelies,” he allows. “Pulling a wheelie was like second nature to me.”

Bigger and faster motorcycles figured in Jose’s life, and at one point he and his pals all rode Kawasaki GPZ1100s. That is, until a not-at-fault accident sidelined him. He quit riding for three years, but then in 1985 a friend showed up on an almost new blue-and-white Suzuki GS1150ES. With only 3,000 miles on the odometer, the Suzuki was for sale and Jose was smitten. “I fell in love with that bike, and my parents helped me finance it to make it mine,” he recalls.

Over the next several years, Jose invested considerable time and money modifying his GS1150ES, turning it into what he calls a crazy street race bike. He installed a longer swingarm, a nitrous kit and bored the engine out to 1,400cc. That was his main ride from 1985 to 1999, but when Jose started a family, his wife didn’t want him on a bike until the kids were off to college, so the GS1150ES was sold.

For the next 20 years or so, Jose would work on motorcycles for friends, but he was nostalgic for his favorite Suzuki. When he had a moment, he’d often snoop around the internet to see if one was for sale, but he rarely ever saw a GS1150ES listed anywhere.

Serendipitously, however, when one of his friends dropped off a GS1150 project that needed reassembly, Jose Googled the bike so he could have a quick look at an image. “That’s when I saw this 1985 GS1150ES for sale in Illinois, just a half-hour from my house,” Jose says. “I couldn’t believe it, it was too good to be true.”

The Suzuki was a one-owner machine that had covered 30,700 miles from new, and the owner was Gordon Siewert, who bought the GS1150ES from Lombard Kawasaki-Suzuki early in 1986. “I had my eyes on the GS1150ES for quite some time,” Gordon remembers. “I had the brochure and an article (the April 1984 Cycle World) that read ‘The Prince of Power.’ I stewed over it for weeks, wondering if I should buy it, as by now I had fallen in love with it. It was just so cool! I had saved the money to buy it with cash, and then in February 1986, the dealer made me a deal on ‘last year’s model.'”

Gordon used the GS1150ES as a weekend rider. A committed motorcyclist, he had other machines he used for commuting duty. On the Suzuki, he says he never felt the need to change a thing, opting to keep it stock because it suited him so well. “I rode it a lot the first 10 years and noticed early on that I had a rare bike: I never passed another blue 1985 on the road,” he says.

As time went by, Gordon found himself wanting to preserve the machine more than ride it. He had cared for and garaged the motorcycle its entire life, but after a great deal of deliberation he finally chose to sell it, replacing it with a 2012 Yamaha FJR1300.

Jose couldn’t believe his luck in finding the machine listed on Cycle Trader. The price was right, but he didn’t have all of the funds. He called his father and asked if he could help out. “When I told him what kind of bike it was that I wanted to buy, he just said ‘Go get it,'” Jose recalls.

But there was one problem. The last of his kids wasn’t quite off to college, and Jose didn’t tell his wife he’d bought the Suzuki. “I hid it from my wife because I didn’t want to lose out on the deal. I kept the secret for about a week, but the guilt was killing me — I’ll never do that again,” Jose says with a sigh. “She wasn’t as upset about the bike as she was that I hadn’t told her.”

With the secret out, Jose began to fettle the GS1150ES. Working in his garage, he left the 1,135cc double-overhead cam inline 4-cylinder engine in the frame, but removed just about everything else.

GS roots

The GS1150ES engine can trace its roots back to the 4-stroke GS750. At that time, Suzuki had been widely known for its production of 2-stroke machines such as the GT series. Due to impending environmental regulations in America and Europe, Suzuki needed a cleaner-running powerplant and developed the 4-cylinder, 4-stroke GS750 that was released late in 1976.

The GS750 featured a stout roller-bearing crankshaft, with one intake and one exhaust valve per cylinder motivated by a pair of overhead camshafts. Suzuki used the same basic platform — with upgraded crankshaft, connecting rods and pistons, and larger valves — in 1978 when it increased the mill to 997cc and launched the standard GS1000 and the slightly sportier GS1000E models.

With the GS1000 motorcycles, Suzuki entered the liter-bike era with machines that went fast, were purported to handle well, and stopped. In 1980, however, the company took the premise even further. The GS engine was taken to 1,074cc and the cylinder head gained an extra two valves per cylinder for a total of four per pot. The cylinder head had a modified pent-roof design that encouraged a better burn of the intake mixture through a feature Suzuki dubbed Twin Swirl Combustion.

But Suzuki wasn’t finished invigorating the GS lineup. In 1981, they used the new and improved engine in the cutting-edge yet controversial Katana. With unforgettable razor-sharp styling, the Katana paved the way for several years of Suzuki styling cues.

The early 1980s were not kind to the motorcycle industry, however, as the U.S. economy softened in 1982. In addition, imported motorcycles of 700cc or more were slapped with new tariffs. As a result, in 1984 Suzuki retrenched and offered only three street and six dirt motorcycles. One of those street machines was the GS1150ES with the half-fairing.

The 4-cylinder GS engine was bored 2mm larger (74mm bore by 66mm stroke) to give an extra 61cc. That 2mm dimension was a common theme — the bank of four CV Mikuni carburetors were each increased 2mm to 36mm units and the intake ports were also increased in size by 2mm. Intake valves were enlarged by 1mm but the exhaust valves did not change in size and remained 23mm in diameter. However, both intake and exhaust valves opened 0.5mm farther into the combustion chamber than on the previous GS1100 engine. Cam timing was changed, the engine was strengthened with 20mm diameter piston wrist pins and an oil cooler was added. And compression was given a slight bump, from 9.5:1 to 9.7:1. “The list of modifications were made,” wrote Cycle Guide magazine in October 1984, “to boost top-end power, yet still retain the low-end and midrange that characterized the 1100.”

But some things stayed the same, including the crankshaft, all internal gear ratios and the cases themselves. The GS1150ES ran from 1984 to 1986, and in addition to the two-tone blue and white it was also available in a red-and-white color scheme.

As noted, Gordon had looked after his GS1150ES, and that made it easy for Jose. All he had to do to the engine was detail it and perform a basic tune-up. Working around the powerplant, Jose also cleaned up the frame, which consists of a variety of round and box-section steel tubes joined together with a single backbone and twin front downtubes. He removed the Full Floater rising-rate rear swingarm and inspected everything, including the Kayaba single-shock, which features four rebound damping settings and five hydraulically controlled preload settings, remotely adjustable via tuning knobs on the left side of the bike just below the seat.

Jose installed a new Metzeler Lasertec tire on the 17-inch rear wheel and also treated the Suzuki to new drive sprockets and a chain. Working towards the front of his GS1150ES, Jose completely disassembled the forks.

When the GS1150ES was introduced in 1984, the forks were different from any Suzuki had previously used. The new units offered improved compression damping, with a four-position adjuster and anti-dive technology that didn’t depend on brake line hydraulic pressure to operate. This, Cycle Guide explained, gave the front dual-disc brake on the new, smaller 16-inch wheel a firmer feel, as previous Suzukis had relied on brake-actuated anti-dive systems. Complementing the rear wheel, Jose mounted a new Metzeler Lasertec tire to the 16-inch front wheel.

What impressed Jose so much about his Suzuki was the condition of all the bodywork, the seat and parts such as the original exhaust system with its black chrome headers and dual mufflers. “It was mint,” he says. “All the factory paint and decals are in immaculate condition, and you never see one of these still fitted with the stock exhaust.”

Even the throttle and clutch cables, footpeg rubbers and handgrips are factory original. What Jose did have to replace were the dry-rotted, rubber-mounted turn signals and the clear windscreen that sits atop the half-fairing with its massive 8-inch headlight. When asked if parts were difficult to find, Jose says he located most everything he needed, new-old-stock, from Suzuki specialist Babbit’s Online.

With the Suzuki cleaned and reassembled, Jose has been adding miles to the clock. “It’s a torque monster with plenty of horsepower,” he says, adding that to atone for chopping and racing his first GS1150ES, he’ll be leaving this one completely stock — no nitrous this time around. So far he’s made one solo trip to Door County, Wisconsin, which had him in the saddle for four hours each direction. “I’ll be riding this bike for a long time,” he says now that he’s no longer living under a cloud of guilt. “And, happily, my wife is a happy passenger around town or on short hour-long rides.” MC

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