- Minimum battery requirement is 800 Cold Cranking Amp (1000 MCA) 107 amp-hr when the outboard is used below 32° F / 0° C (Yeah, I know you said it's not a battery problem...).
- Make sure battery cable connections are clean (no corrosion), and tight. Wing nuts must NOT be used to connect battery cables to the battery. The requirement calls for hex nuts with lock washers.
- Lastly, 4 gauge cable is too small for a 16 ft. run. The Evinrude Installation Guide calls for 1 gauge battery cables if the run is 16 to 20 ft. The 4 gauge cable is recommended ONLY up to 10 ft.
You alluded to something about temperature too, so:
- If the outboard will be operated in temperatures below freezing (32°F, 0°C), use Evinrude/Johnson
- Check the "specific gravity" of each cell in the battery or have the battery "load tested" by your dealer. A bad cell in the battery can cause hard starting in colder weather.
- You said the voltage drop between the battery and starter lug is "small". How small? 0.25 V, 0.7 V?? A voltage drop test is outlined in the service manual. This test checks each "leg" of the circuit to determine if / where in the starting circuit a specific problem might be.
I'm not saying you don't have a starter issue, but if you're using 4 ga. battery cable to go 16 ft, you definately have a battery cable problem...