| Component | Specification |
|---|---|
| Production Years | 1974-1979 |
| Transmission Oil | SAE 10W-40 / 20W-40 (JASO-MA) (0.75 L) |
| Tire Size (Front/Rear) | F: 2.75-18 4PR / R: 3.00-18 4PR |
| Tire Pressure (Solo) | F: 1.6 bar (23 psi) / R: 2.0 bar (28 psi) |
| Spark Plug | NGK B8HS (Gap: 0.6mm-0.7mm) |
| Battery Type | 12N5-4B |
The Suzuki GT 125 holds a unique place in engineering history as one of the few 125cc motorcycles of its era to utilize a parallel-twin two-stroke engine. While its competitors often relied on single-cylinder configurations for simplicity, Suzuki’s choice to use two 62cc cylinders allowed for a higher redline and a smoother power delivery that earned it the reputation of a ‘mini-superbike’ in the mid-1970s.
Engineering Overview
The GT 125 (GT-125) was part of the ‘Grand Touring’ series, benefiting from Suzuki’s Ram Air System—a shroud over the cylinder heads designed to force air over the cooling fins. This ensured thermal stability even during high-RPM operation. Despite its small displacement, the twin-carburetor setup demanded precise synchronization to maintain its 14hp peak output.
Maintenance Guide
1. Lubrication System
The GT 125 uses the Suzuki ‘CCI’ (Cylinder Crankcase Injection) system for engine lubrication. However, the transmission requires a separate supply. We recommend 0.75 Liters of high-quality SAE 10W-40 or 20W-40 JASO-MA oil. Using oil with the JASO-MA certification is critical to prevent clutch slippage, as modern automotive oils often contain friction modifiers that are incompatible with the GT 125’s wet clutch.
2. Ignition & Electrical
Maintaining a strong spark is vital for two-stroke efficiency. The NGK B8HS is the factory-standard plug. Ensure the gap is set strictly between 0.6mm and 0.7mm. The electrical system is powered by a 12N5-4B battery; given the age of these machines, checking the charging circuit’s voltage is recommended to prevent premature battery failure.
3. Tires and Handling
The lightweight frame of the GT 125 is sensitive to tire pressure. For solo riding, maintain 1.6 bar (23 psi) in the front and 2.0 bar (28 psi) in the rear. If carrying a passenger, the rear pressure should be increased to 2.3 bar (33 psi) to maintain stability and prevent tire overheating.
Editor’s Verdict
The Suzuki GT 125 is a masterclass in small-capacity engineering. For the modern collector, it offers a visceral two-stroke experience that modern bikes cannot replicate. Regular attention to the spark plug condition and gearbox oil levels will ensure this 1970s icon remains roadworthy for decades to come.