| Quick Specs: Honda SL 125 S (SL125S) | |
|---|---|
| Production Years | 1971 – 1973 |
| Engine Type | 122cc Single-cylinder OHC 4-stroke |
| Engine Oil | SAE 10W-40 (JASO MA) – 0.9 L |
| Spark Plug | NGK D8EA |
| Battery | 6N6-3B (6 Volt) |
| Front Tire | 2.75 – 21 (1.5 bar / 21 psi) |
| Rear Tire | 3.25 – 18 (1.8 bar / 25 psi) |
While many vintage motorcycles of the early 1970s were simply road bikes with high-mounted exhausts, the Honda SL 125 S Motosport holds a unique place in engineering history as one of Honda’s first dedicated dual-sport machines designed with a purpose-built diamond frame. Unlike the CL-series “Scramblers,” the SL125S featured a geometry specifically optimized for off-road stability and increased ground clearance, marking the true evolution from street-based conversions to authentic trail machinery.
Engineering Heritage & Performance
The SL 125 S is powered by a robust 122cc overhead cam (OHC) single-cylinder engine. In an era dominated by two-strokes, Honda’s commitment to the four-stroke cycle provided a linear power delivery and superior fuel efficiency. The engine is known for its durability, provided that the centrifugal oil filter is kept clean—a common oversight for novice restorers.
Maintenance Essentials
Lubrication System
The SL125S utilizes a wet-sump lubrication system. For optimal protection of the vintage gearbox and wet clutch, we recommend a high-quality SAE 10W-40 oil that meets JASO MA specifications. The total capacity is 0.9 Liters. Because these engines lack a modern disposable paper filter, regular oil changes every 1,000 miles are critical to prevent sludge buildup.
Ignition and Electrical
The electrical system is a traditional 6-volt setup powered by a 6N6-3B battery. For consistent combustion, the NGK D8EA spark plug should be gapped to 0.6-0.7mm. Owners should regularly inspect the contact breaker points; pitted or dirty points are the primary cause of hard starting and erratic idling in this model.
Chassis and Tires
The SL 125 S features a 21-inch front wheel, which was a significant upgrade for off-road handling compared to its predecessors. For mixed-terrain use, maintain the front 2.75 – 21 tire at 1.5 bar (21 psi) and the rear 3.25 – 18 tire at 1.8 bar (25 psi). These pressures provide the necessary footprint for trail traction while maintaining stability on paved surfaces.
MotoSpecsLab Verdict
The Honda SL 125 S remains a pinnacle of vintage dual-sport engineering. Its mechanical simplicity makes it an ideal candidate for collectors and DIY mechanics. By adhering to the 0.9L oil capacity and maintaining the 6V electrical system, this “Motosport” legend continues to offer a reliable and nostalgic riding experience.