Re: 1979 140HP Starting problem
The power to the starter is almost directly from the battery, with only the starter solenoid in between. Most problems are [1[ bad battery cables, [2] poorly grounded starter or battery cable, or [3] bad solenoid.
After starting, feel the cable contacts at the battery, the engine and the solenoid; resistance usually telegraphs itself by heat.
If all of that checks out OK, you might want to take the starter to a shop for a check-up or rebuild.