Outboard Motor Electrical Systems

By FLC & WCCB member Dick Newcomb

Testing an outboard motor electrical system is quick and easy. Replacing the components can be a challenge!

Good 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.

The 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.

I 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.

With 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.

Pre-1976 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.

You 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.

Most outboards have two sets of contact points so you will have to do this twice.

Now 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.

If you still don't have spark or if you don't have an access opening, your next task will be to remove the flywheel.

This 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.

With 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 stator).

You 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.

OMC, 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.

If 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.