Troubleshooting Guide for Outboard Motors
Fuel, ignition, compression, cooling, and winterization basics for diagnosing the most common marine engine problems.
The Fuel System
The fuel system on an outboard, being a breed of its own, can confuse the average person during diagnosis. For example, an anticipated fuel problem can sometimes actually be ignition related, or even compression related. This is why it is always a good idea to check the simple things first.
If fire is good to all cylinders, and compression is within range showing no more than 15 lbs. difference from cylinder to cylinder, then the problem would most likely be fuel related. Either stopped up carbs, weak or bad fuel pump, low or no compression on cylinder supplying pulse to fuel pump, a bad squeeze bulb, tank not venting, stuck anti-syphon valve on tank, loose fuel line connections, etc., could all be causing a problem you may be encountering.
Upon diagnosis, just remember to check all three required elements before you simply start replacing parts by trial and error. We receive many inquiries on how to test the Johnson/Evinrude VRO oil injection system. Below are two methods to troubleshoot problems with them.
A. An intermittant "beep...beep...beep" sound has to do with oil injection. A steady continuous "beeeeeeeeeeeeeeeeeep" has to do with overheating. Oil injection on all outboards produces an intermittant beep when there is either a problem with your motor not getting oil, oil tank level sensor is bad, or your oil level in the tank is low. When the oil tank is low, you have roughly 30 to 45 minutes running time before being empty.
A. Sure....check these links: Standard non oil injection fuel pumps | (Carb section coming soon!)
Ignition Systems
Ignition systems can be the "tough" problems to figure out for the average person, and they can cause a very wide variety of symptoms. Outboard ignition systems are very different than those of the automotive type.
What is causing your motor to not start, cut out, run good to a specific RPM, or overall run poorly? First make sure to check that timing is advancing properly and fully, there are no broken damaged or bare wires, nothing shorted out, and no rogue arching spark around plug wires.
If you are having an ignition component problem, special equipment is usually required for testing most system parts such as stators, triggers, and power packs, so you may opt to let a qualified technician diagnose these problems for you instead.
Don't listen to advice from the guy next door of "try changing this, or try changing that". Trial and error replacement of ignition parts can get VERY EXPENSIVE if you don't get it right the first time, and dealers or parts houses will not take returns on electrical parts.
If you decide on diagnosing and repairing the outboard ignition system yourself, and you have access to testing equipment, then check out the following links that provide valuable information to help you along.
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Compression
Compression is the heart of an outboard. If one or more cylinders are damaged due to improper timing settings, lean fuel condition, overheating, or stuck rings from carbon buildup, your outboard is about to become history.
Does a compression test alone always determine that my outboard is in good shape? Suprisingly the answer is "no". A good compression reading does not completely determine internal conditions. To correctly diagnose condition of pistons, rings, and cylinders, a leakdown test should also be performed.
Using a quality leakdown tester, each cylinder should not show more than 10% loss. If any do, there is certain to be an internal problem in the making. For example, a compression reading of 120 lbs would be viewed upon as a good cylinder by the average person. This may or may not be the case.
If a leakdown test of the same cylinder indicates say...20% to 25% or more leakage, it would be a good bet that excessive wear, scored cylinder, the cylinder scratched, and/or the rings stuck or damaged in a way that does not show up with a simple compression check.
In any case, wear or damage is present and advisedly requires attention before further damage and/or exceptionally poor performance and efficiency results. Most common effects from diagnosis of excessive leakdown would be in the idle range of the motor.
Cooling System
Cooling system condition is critical for an outboard to live. It only takes a few seconds, especially running at high RPM's, for an overheat situation to kill an outboard powerhead.
Do not rely on a water hose to check your impeller. A water hose will pressurize the system, overriding the impeller, and giving a false sense that the impeller is ok.
Winterization
Winterization is commonly ignored by many when it comes to outboards. "The water drains itself so why bother"? By spending an hour with your investment, you can prevent 90% of the common problems that occur with an outboard motor.
In the fall when you figure your out on the water for the last time for the season, add fuel conditioner to your fuel tank and let it circulate throughout your entire fuel system before you put the boat up for winter. This will help prevent stale gas and varnished carbs in the spring.
Following this procedure will eliminate the need to run the motor out of gas (which you cannot do with todays oil injected motors). Also top off your fuel tank at the same time to prevent condensation from forming in the fuel tank.
When you get the boat home, remove the air box cover and with the throttle in wide open position, spray fogging oil in the carbs. Remove plug wires and crank the motor a few revolutions. This will distribute the oil through the internals of the powerhead and protect them from corrosion while stored out of use.