Johnson Model: J10RC0M (or J10RCOM) Year Determination The model J10RC0M / J10RCOM does not follow the cleanest form of the standard INTRODUCES year code, which makes an exact year slightly less straightforward. However, based on very similar models in the Johnson parts catalogs (especially J10RC series): Most closely matching models (J10RCUE, J10RCCD, etc.) fall in the 1987–1988 range. The “RC” portion indicates a Rope start / Commercial / CD ignition style 9.9–10 HP motor. The trailing “0M” or “OM” is most likely a production run / suffix letter rather than the year code. Most probable year: 1987 or 1988
Outboard Ignition Coil Testing (For Johnson / Evinrude 9.9–15 HP and similar 2-stroke motors) You can test the ignition coils with a basic digital multimeter (ohmmeter). Here’s the practical procedure. Tools Needed Digital multimeter set to Ohms (Ω) Spark plug wire pliers or needle-nose pliers Clean rag Safety First Disconnect the battery (if equipped) or remove the spark plug wires. Make sure the engine is not running and the kill switch is in the OFF position. 1. Primary Winding Test (Low Resistance) Disconnect the small primary wire(s) from the coil (usually a single spade terminal). Set the multimeter to a low ohms scale (200 Ω or auto-ranging). Touch one probe to the primary terminal. Touch the other probe to a good engine ground (or the coil’s metal mounting tab/core). Expected reading (typical for these motors): 0.1 – 1.5 ohms** (most common range is 0.5 – 1.0 Ω) Reading of 0 or very close to 0 → shorted primary → bad coil Reading of OL (infinite) → open primary → bad coil 2. Secondary Winding Test (High Resistance) Keep the primary wire disconnected. Set the multimeter to a higher ohms scale (20kΩ / 20,000 Ω). Place one probe on the primary terminal. Place the other probe inside the spark plug boot (touching the metal terminal). Expected reading: 3,000 – 8,000 ohms** (3k – 8k Ω) is common on many older Johnson coils Some models fall in the 225 – 350 ohms range (especially later CD ignition coils) Outside this range or OL → bad secondary winding → replace the coil 3. Short-to-Ground Test One probe on the primary terminal Other probe on the metal core/laminations of the coil Should show OL (no continuity). Any reading means the coil is shorted to ground. Quick Tips for Your Motor On 9.9/10 HP Johnsons of this era, the coils are usually mounted under the flywheel on the magneto plate. Always test both coils (most of these motors have two). A coil can pass the resistance test and still be weak under load. The best final check is a spark tester (in-line or gap-style) while cranking. Would you like the typical resistance values specifically for the charge coil / stator as well (common cause of no-spark on these motors)?