# YL-1 Specification Reference
## Serial: engine L1-47603, frame Y33-47603 (1966 YL-1 Twin Jet 100)

The year is taken from other YL1s: frames Y33-29698 and Y33-46101 are sold as 1966 bikes. Yamaha did not stamp a date.

**Source:** Intertec Publishing — *How to Fix Your Yamaha Two Cylinder, Two-Stroke Motorcycle* (1975). OCR extracted from `2Cyl2StrMan_extracted.txt`. Pages cited.

> Values marked ✅ are confirmed directly from the Intertec manual OCR.  
> Values marked ⚠️ are estimates pending verification from the printed manual or a model-specific source.  
> Values marked ❌ were found to be incorrect in earlier documentation and have been corrected here.

---

## Engine

| Parameter | YL-1 Value | Unit | Source |
|---|---|---|---|
| Displacement | 98 | cc | p.11 ✅ |
| Bore | **38** | mm | p.11 ✅ (was incorrectly listed as 43mm ❌) |
| Stroke | **43** | mm | p.11 ✅ (was incorrectly listed as 33.6mm ❌) |
| Number of cylinders | 2 | — | p.11 ✅ |
| Engine lubrication | Oil pump (Autolube injection) | — | p.11 ✅ |
| Compression ratio | ~7.3:1 | — | ⚠️ estimate — verify |

---

## Ignition & Electrical

| Parameter | YL-1 Value | Unit | Source |
|---|---|---|---|
| Spark plug | NGK B7-HS | — | p.11 ✅ |
| Spark plug gap | 0.6–0.7 | mm (0.024–0.027 in.) | p.11 ✅ |
| Breaker point gap | **0.3–0.35** | mm (0.012–0.014 in.) | p.11 ✅ |
| Ignition timing | **1.8 mm BTDC** | mm | p.11 ✅ |
| Electrical system voltage | **12** | V | p.11 ✅ — ⚠️ contradicts commonly cited 6V; physically verify battery |
| Battery ground | Negative | — | p.11 ✅ |

### Voltage note
All three models (YL-1/YL-1E, HS-1/HS-1B, LS2) are listed as 12V in the spec table on p.11. The commonly stated 6V assumption may apply only to the earliest production (pre-1967) Japanese-market YL-1. Verify by reading the battery itself or checking open-circuit voltage (~12.6V = 12V system; ~6.3V = 6V system).

---

## Carburetion

| Parameter | YL-1 Value | Unit | Source |
|---|---|---|---|
| Carburetor type | Mikuni VM (round-slide, two carbs) | — | p.11 ✅ |
| Idle speed | **1200–1500** | RPM | p.11 ✅ |
| Idle mixture initial setting | **2.5 turns open** | — | p.11 ✅ |
| Valve needle clip position | **3rd groove from top** | — | p.11 ✅ |
| Float level | **23 mm** (0.906 in.) | mm | p.11 ✅ |
| Main jet | Not recovered from OCR | — | ⚠️ verify from printed manual |
| Pilot jet | Not recovered from OCR | — | ⚠️ verify from printed manual |
| Needle jet | Not recovered from OCR | — | ⚠️ verify from printed manual |

> The jet size columns in the Intertec manual (p.11) were in a compressed table layout that the OCR did not capture for the YL-1 column. HS-1 main jet was captured as #70, pilot jet #20 — YL-1 values should be similar but must be confirmed.

---

## Engine Measurement Limits

| Parameter | Spec | Unit | Source |
|---|---|---|---|
| Standard bore diameter | **38.00** | mm | p.11 ✅ (bore=38) |
| Piston skirt to cylinder clearance | **0.035–0.040** | mm (0.0013–0.0016 in.) | p.13 ✅ |
| Max cylinder taper or out-of-round | **0.05** | mm (0.002 in.) | p.13 ✅ |
| Piston ring end gap | **0.10–0.30** | mm (0.004–0.012 in.) | p.13 ✅ |
| Ring clearance in groove | **0.03–0.07** | mm (0.0012–0.0027 in.) | p.13 ✅ |
| Con-rod side shake (big end) | **0.8–1.0** (replace if >2.0) | mm | p.13 ✅ |
| Con-rod side clearance (between counterweights) | **0.1–0.3** | mm | p.13 ✅ |

---

## Torque Values

| Fastener | Torque | Source |
|---|---|---|
| Cylinder head stud nuts | **103 kg-cm = 90 in-lb = 7.5 ft-lb = 10.1 N·m** | p.13 ✅ |
| Cylinder base nuts | ⚠️ estimate ~1.0–1.2 kgf·m (7–9 ft-lb) | verify from manual |
| Flywheel nut | ⚠️ estimate ~3.5–4.0 kgf·m (25–29 ft-lb) | verify from manual |
| Crankcase bolts | ⚠️ estimate ~0.8–1.0 kgf·m (6–7 ft-lb) | verify from manual |

---

## Oil Pump (Autolube)

| Parameter | YL-1 / YL-1E | Unit | Source |
|---|---|---|---|
| Pump plunger clearance (A) | **0.25–0.35** | mm (0.0098–0.0138 in.) | p.12 ✅ |

---

## Clutch

| Parameter | Value | Source |
|---|---|---|
| Hand lever free play | **2–3 mm** (¼ in.) | p.12 ✅ |
| Clutch spring free length (YL-1/YL-1E) | **25 mm** (0.98 in.) | p.11 ff. ✅ |
| Clutch friction disc thickness | 4 mm nominal (replace if < 3.9 mm) | p.11 ff. ✅ |

---

## Lubrication — Fluid Capacities

| System | Fluid | Capacity | Drain interval | Source |
|---|---|---|---|---|
| Front forks | **SAE 30 motor oil** | **130 cc per leg** | Every 4,000 miles | p.13 ✅ |
| Gearbox / transmission | **SAE 30 motor oil** | **750 cc** | Every 2,000 miles | p.12 ✅ |
| Autolube tank | Air-cooled 2-stroke oil (JASO FC/FD) | Fill to mark | Monitor level | p.12 ✅ |

---

## Chassis & Wheels

| Parameter | YL-1 Value | Unit | Source |
|---|---|---|---|
| Tire size (both) | **2.50 × 17** | — | p.11 ✅ |
| Tire pressure — front | **1.5 kg/cm²** (22 psi) | — | p.11 ✅ |
| Tire pressure — rear | **1.9 kg/cm²** (28 psi) | — | p.11 ✅ |
| Rear chain size | **#420** | — | p.11 ✅ |
| Rear chain free play | **20 mm** | mm | p.11 ✅ |
| Number of speeds | **4** | — | p.11 ✅ |
| Weight (approx.) | **82 kg** (180 lb) | kg | p.11 ✅ |

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## Items Still Requiring Manual Verification

| Item | Status | Notes |
|---|---|---|
| Main jet size (YL-1) | ❌ Not in OCR | Check printed manual p.11 carb table |
| Pilot jet size (YL-1) | ❌ Not in OCR | Check printed manual p.11 carb table |
| Needle jet part number (YL-1) | ❌ Not in OCR | Check printed manual p.11 carb table |
| Cylinder base nut torque | ⚠️ Estimated | Verify from manual |
| Flywheel nut torque | ⚠️ Estimated | Verify from manual |
| Crankcase bolt torque | ⚠️ Estimated | Verify from manual |
| Electrical voltage | ⚠️ Manual says 12V, but physically verify | Read battery or measure open-circuit voltage |
| Compression ratio | ⚠️ Estimated 7.3:1 | Verify from manual or factory spec sheet |

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*Generated from OCR extraction of Intertec manual + manual review of pages 11–13.*  
*Last updated: 2026-02-21*