1977 115 hp, in line 6 cylinder, stopped suddenly with no hesitation

[tavacska]

The motor is 1977 115 hp, in line 6 cylinder, with distributor.

Last week, I tested the motor at home before heading to the bay. Start easily.

But at the ramp, the motor is very hard to start. After start the motor, the boat went out of the ramp site and the motor stopped suddenly without any hesitation. Then it was again very hard to start. But it started finally but dies again very quickly. It won't start any more since then, and we are pulled to ramp by a coast guard.

The battery was on 11.2 volt as the fish finder showed, which is always 0.5 volt less than detected directly by digital multimeter.

After getting home, the motor can be started with the battery and still dies suddenly.

What could be the reasons? Where should I start first?

 

[Canufixit2]

when you get it started try spraying some starting fluid in each carb and see if it stays run. IF so I''d clean the carbs.

 

[Chris1956]

The motor wiring on those older motors is usually rotted out by now, unless it has been changed. That motor needs +12V to the red and adjacent white wires on the switchbox, to have spark.

The CDIElectronics site has an ign test you can run. It will test everything but the trigger. Triggers can be intermittent before they fail.