1974 Johnson 15 HP Outboard Specs & Part Numbers
Engine Specifications Quick Box
| Model / Series: | 15R74M |
| Fuel Mix Ratio: | 50:1 |
| Spark Plug: | Champion L77JC4 |
| Plug Gap: | 0.030 in |
| Ignition Type: | Low Tension Magneto |
| Point Gap: | 0.020 in |
Direct Replacement Part Numbers
Use these cross-reference numbers to order replacement components:
- Carburetor Rebuild Kit: Sierra 18-7010 (OEM 398532)
- Water Pump Impeller: Sierra 18-3059 (OEM 395289)
- Ignition Coil: Sierra 18-5181 (OEM 581407)
- Fuel Pump Diaphragm: Sierra 18-7800 (OEM 397274)
Quick 3-Minute Diagnostic Steps
- Check spark strength using an inline spark tester; it must jump a 1/4 inch gap with a crisp, blue snap.
- Verify fuel delivery by ensuring the primer bulb becomes firm, checking for fuel at the carburetor bowl, and confirming fresh 50:1 fuel mixture.
- Perform a compression test on both cylinders; readings should be above 90 PSI and within 10% of each other.
- Inspect and clean the ignition points under the flywheel, ensuring they are free of oxidation and precisely gapped to 0.02020 inches.