Evinrude 150 stopping at low RPMs

I have a 1998 or so Evinrude 150 with a 20' aluminum boat (Princecraft Pro-V). The boat has four downriggers on it. When trolling at low RPMs (just above idle), the engine shuts off after 10-15 minutes or so. The following are the facts:

1) Battery is new.
2) Battery is fully charged.
3) Voltage at low RPMs is very low - below 12.4V. Voltage is so low the fishfinder sometimes shuts itself off due to low voltage.
4) Voltage at high RPMs is above 14V.
5) The gas pump bulb is soft when engine dies.
6) I can squeeze the gas pump bulb and restart the engine, rev it a little, and run for another 3-5 minutes before it dies again.

This has been going on for a few years. It sounds to me like the alternator is now sufficiently charging at RPMs just above idle. What voltage should the alternator be outputing at RPMs just above idle?

Any other ideas? Thanks.

Re: Evinrude 150 stopping at low RPMs

What are the rpm numbers when trolling,
my 150 will idle til the cows come home at around 700 rpm.
But I find the boat is moving too fast for trolling and I need a trolling motor.
Maybe you're trying to idle it down too low.

The factory manual says something about setting the plug gap wider for extended trolling, .30 instead of .20 and be sure to use the correct Champion plugs only. Or is that .030 ? whatever. Just add .10 more what ever it is.

Re: Evinrude 150 stopping at low RPMs

Champion Plugs. true, a lot of trolling, open gap an additional .005 or .010.
150, 175 (60? V6) 1991 & newer QL78YC (see note 3) .030
150 Commercial (60? V6) 1993 - 2001 QL78YC (see note 3) .030

also make sure you low speed jets are clean. the bulb is suppose to be soft once the fuel pump starts pumping.

charging voltage has nothing to do, with the running voltage. the motor runs off the stator, not the battery.

you need separate, house batteries to run your electronics and accessories. you can install a battery selector switch, to charge the house battery, when running fast. post the battery switch question in the electrical forum.

the motor puts out, little charge running at idle speeds.