Although this model looks very similar to the previous ’89 model many changes were made. The 1990 Suzuki GSX-R750L was considered possibly the best of the oil-cooled GSX-R750 models. The 1990 Suzuki GSX-R750 featured changes to the engine, suspension, body work, brakes and chassis. This was the first GSX-R to be fitted with inverted forks as standard (USA models retained the conventional forks until 1991), and returned to the bore and stroke dimension of the original long-stroke engine.
The engine returned to the 749 cc engine bore and stroke dimensions of the original long-stroke engine but still maintained the 13,000 rpm redline. It now featured new conrods, lighter pistons, smaller valves than the 1988/89 engine but larger than the 1985-87 engine and used larger carburetors. The new Mikuni model BST38SS “slingshot” carburetors were 38 mm diameter and featured an additional high-speed circuit (circuit was blocked in USA models) and the slide breathers were now divorced from air box. The exhaust system was also changed, gone were the dual silencers and replaced with one stainless steel silencer on the right side and the transmission output shaft was lengthened to accommodate a wider wheel. A new curved oil-cooler design with a large capacity oil pump and oil lines (attached to the oil pan similar to the original 85-87 engines) were installed. Horsepower was up to 115 hp at 11,000 rpm while weight was down to 193 kg.
The frame was changed for 1990 and used some of the features from the ’89 GSX-R1100 frame with the rake was now 25.5 degrees and wheelbase 55.7 inches (1,410 mm). The front suspension now had 41mm inverted forks, the triple clamps (yokes) and handlebars were changed to accommodate the new forks. The rear suspension featured a new shock and swingarm, the rear shock now had a remote reservoir and damping adjustment and the revised swingarm now featured cast ends for the axle adjustment. With the rear wheel widened to from 4.4 inches (110mm) to 5.5 inches (140 mm) but the tire size remained the same. A non-adjustable steering damper was added which attached from the left frame rail to a clamp on the left fork (US models did not receive the damper but the frame had the tapped mounting holes). The rear sprocket carrier and sprocket changed fomr a five to a six-bolt design. The front brake rotors changed from a cross drilled hole design to a slotted design.
The body work changed slightly also with the side vents becoming less rectangular and in a slightly different position. A new fender was also used with the inverted forks (except US).
The bike Suzuki GSXR 750 1990 was possibly the best oil cooled models also the last of the “Oil Cooled” the GSX-R range.
Major changes in this new model included a 41mm inverted and above all, a return to long-stroke engine fork (short-stroke engine was not as good for competition, but was good for the road).
The very long-stroke engine (70 x 48.7mm) of the ‘double R’ became standard, with new pistons to match the new design of the combustion chamber in the cylinder head and strengthen the cranks. Suzuki threaded rod screws into the bars themselves, this saved the weight associated with nuts and washers.
Based on the invaluable experience gained in racing, the model Suzuki GSXR 750 1990 received many features of the racing version of Suzuki GSXR 750R at an affordable price.
Other changes included an exhaust system in stainless steel 4-2-1, steering damper, carburetors 38mm Slingshot small valves (2 K the standard model but still 2mm smaller than the larger model RK mm) rods new, lighter pistons, oil pump high capacity and larger oil radiator.
The rim of the rear wheel had expanded and equipped with Michelin radial tires, became the standard 17 × 5.5 “. The 41 mm inverted forks and rear shock became fully adjustable.
The front brake discs and were thicker compared slotted drilling units of the previous model, the Suzuki GSXR 750 1988.
The power of the bike Suzuki GSXR 750 1990 reached 115 hp at 11,000 rpm, while the weight was reduced to 193 kg.
Suzuki GSX-R 750 1990 SPECIFICATIONS Suzuki year code 1990: L Colours Pearl Still White / European Blue No.2 (3SL) Pearl Still White / Marble Italian Red (3RZ) Pearl Novelty Black / Urban Gray Metallic (3CG) Dimensions and curb weight Overall length: 2,070 mm (81.5 in) Overall width: 730 mm (28.7 in) Overall height: 1,135 mm (44.7 in) Wheelbase: 1,420 mm (55.9 in) Ground clearance: 130 mm (5.1 in) Empty weight: 193 kg (425 lbs) Engine Engine Type: 4 stroke, oil cooling, DOHC Number of cylinders: 4 cylinders Calibre: 70.0 mm (2.756 in) Stroke: 48.7 mm (1.917 in) Displacement: 749 cc (45.7 cu in.) Carburetor: MIKUNI BST38SS Air filter: Paper element Starting system: Electric Lubrication system: Wet Carter Drivetrain Clutch: Wet, multiplate oil Transmission: 6-speed constant Gear Gearshift pattern: 1 reduction, 5x Primary reduction ratio: 1.744 (75/43) Gear Ratio: First: 2,866 (43/15) 2nd: 2,058 (35/17) 3rd: 1,650 (33/20) 4th: 1,428 (30/21) 5th: 1,260 (29/23) High: 1,120 (28/25) Final reduction ratio: 2.800 (42/15) Drive chain: RK TAKASAGO 50GSVZ1 or DAIDO DID 50VA7, 108 links Chassis Front suspension: Inverted telescopic, coil springs, adjustable preload, damping oil. Rear suspension: articulated type, coil springs, damping oil / gas, adjustable preload fully adjustable shock compression and rebound. Fork travel: 120 mm (4.7 in) Rear wheel travel: 136 mm (5.35 in) Steering angle: 30 ° Caster angle: 65º 30 ‘ Filmed: 94 mm (3.7 in) Turning radius: 3.1 m (10.2 ft) Front brakes: Double disc brake Rear brake: single disc brake Front Tire Size: 130/70 ZR 17, tubeless Rear Tire Size: 170/60 ZR 17, tubeless Electrical Equipment Ignition Type: Electronic ignition (Transistorized) Ignition timing: 7th BTDC at 1500 rpm Spark plug: NGK CR10EK Battery: 12 V 36.0 kC (10 Ah) / 10 HR Generator: Three-phase AC generator Main fuse: 30A Fuse: 15/15/15/10/10 A Headlight: 12 V 60 / 55W x 2 Flashing light 12 V 21 W Light: 12 V 5 W Brake / Rear: 12 W x 2 5/21 V Speedometer Light: 12V 1.7W Light Tachometer: 12V 1.7W x 2 Neutral indicator light: 14V 3W Indicator light beam: 14V 3W Indicator light turn signal: 14V 3W Oil pressure indicator light: 14V 3W Capabilities Fuel tank, including reserve: 21 l (5.5 US / Imp gal) Engine oil: oil change: 3,000 ml (3.2 / 2.6 US / Imp qt) with filter change: 3.300 ml (3.5 / 2.9 US / Imp qt) Repair: 3.900 ml (4.1 / 3.4 US / Imp qt) Fork oil 419 ml (14.2 / 14.8 US / Imp oz) Refrigerant: 2,550 ml (2.7 / 2.2 US / Imp qt)