Motor Electrical Systems
FLC & WCCB member Dick Newcomb
Testing an outboard motor electrical system is quick
and easy. Replacing the components can be a challenge!
spark is critical and is "element number one" in a
good-running motor. Without spark there is no sense
attempting any other repairs on an outboard motor.
best way to test for spark on your outboard is with
a spark checker (see picture). These can be simple,
testing one plug at a time, or multiple. They can
range in price from a few dollars to about $80. The
one I have can test four plugs at once and costs about
$40. I wouldn't be without it.
remove the spark plugs from all the cylinders when
I test for spark. This relieves the compression and
makes it a lot easier to crank the motor. You'll really
appreciate that if you are pull-starting a four cylinder
or larger outboard. Even the 30-40 HP two-cylinder
engines are very hard to pull-start while also paying
attention to your spark tester.
the spark tester's wires properly connected to the
spark plug wires and the ground clip securely connected
to the engine block, you should get a nice blue spark
between the points on the tool and its base when you
turn the engine over. It should be strong and obvious.
If in doubt, try your tester on an engine you know
to be running well to become familiar with what it
should look like. If the spark is weak or missing
altogether, it's time to move on to the components.
outboards generally have electrical systems that consist
of a magnetized flywheel, coils, contact points, and
a condenser. If you are reeeeeally, lucky the only
thing wrong will be that the contact points are fouled
with oil or a bit of corrosion. Many of the mid-50s
and later outboards, have a viewing/access opening
in the top of the flywheel. You don't have a lot of
room to work in, but that access is there so you can
clean the contact points with some fine emery paper
and check them for gap.
I better explain that. As the flywheel travels around
there is a lobe (bump) on the center that pushes on
the contact point set as it goes by. This opens the
points breaking the flow of electricity to the spark
plug, much like a light switch. Ideally, the points
should have a space between them (gap) that is specific
for each style of engine. Most are set around .020
of an inch.
can purchase a gap checker (see picture) at any auto
supply store. Turn the flywheel slowly by hand and
watch for the points to open. When they start to close
again, stop. Redo this a few times until you catch
the points at their maximum opening. There is an adjustment
screw in the base of the contact set. It will be in
an oval opening in the base of the set. You slowly
turn this and place your correct shim from the gap
checker in between the points. There should be a little
resistance when you pull the shim out.
outboards have two sets of contact points so you will
have to do this twice.
try your spark checker again. With luck you'll get
a good spark. If a motor has been sitting in storage
for some time, this is usually the cure.
you still don't have spark or if you don't have an
access opening, your next task will be to remove the
can be a challenge! You will need a flywheel puller
(see picture). The flywheel has three predrilled and
threaded bolt holes in the center. Some-times you
have to remove a cover which may be just a cover,
or it may be part of the recoil for the rope pull-start.
If you have never done this, I'd recommend calling
someone who has and learn from their experience. From
then on, you'll know how to do it. I'd be glad to
help anyone learn about this.
the flywheel off, you will see the stator, which holds
all the components. You can now replace the points,
condensers and coils fairly easily. The most critical
component is the coil (see picture of typical OMC
need some specialized equipment to test coils. I have
one of theses coil testers, so if you would like to
check a coil, I'll be glad to help.
Johnson & Evinrude coils are not expensive and are
available at NAPA or your local Marina for about $15.-20.
each. Mercury coils are much pricier ($60.ish), and
probably will have to be ordered through a dealer.
The Antique Outboard Motor Club, Inc. has folks who
specialize in these parts. Condensers are inexpensive
as are the contact points. NAPA has most all of these.
you are restoring/repairing your outboard, I'd recommend
you replace all the electrical components. They are
not that expensive, and since you've already done
the hardest part (pulling the flywheel), why not replace
all the components with new ones? While you are at
it, also replace the spark plug wires (with solid
core wire, if you can get it) and the spark plugs,
too. If you plan on using your engine throughout the
summer, replace the spark plugs at the start of each
season and carry a set of new ones with you. It is
the cheapest insurance you can buy.