How to Troubleshoot Your 2-Cycle Outboard Motor

Two-cycle outboard motor problems can be frustrating, costly and potentially dangerous so learning how to troubleshoot and repair your outboard motor can be a real benefit. Having a problem with your outboard motor when you are ready to spend a day fishing or skiing or tubing can be discouraging not only to the boat owner but to those who were planning on taking part in the fun. Discovering you have an outboard motor problem when you are far from shore and a squall line is approaching can turn an inconvenience into a tragedy. No matter what the situation you can troubleshoot your outboard motor using some of these basic tests.

There are a number of different manufacturers and models of outboard motors so a detailed analysis of specific problems is beyond the scope of this article. Assuming you want to determine the cause of the problem suffice it to say that a key factor in all outboard troubleshooting is to control the various parameters you might change when you troubleshoot and avoid the temptation of changing too many at one time. Another technique to avoid is to change a setting and not change it back to the original state if no change in performance is found. This would especially apply to many outboard ignition and carburetor settings. Other changes to your outboard such as putting in new, properly gapped spark plugs or changing to fresh gas are not necessary to reverse once done.

Most outboard problems present some symptoms before the outboard quits totally. The experienced powercraft boater should become familiar with their outboard and constantly listen to it for any subtle variations in sound and also be aware of other differences experienced when starting it, trolling, accelerating or running at WOT (wide open throttle). When it comes time to troubleshoot your outboard motor being aware of subtle variations in the way it sounds can lead you to narrow your search for the problem.

It is common knowledge that fuel, ignition, carburetion and cooling are some of the primary requirements for a functioning outboard motor. A problem in one of these areas can lead to outboard motor problems and the need to do troubleshooting. When trying to analyze a problem with an outboard motor some problems can be caused by a number of sources. For example a lack of acceleration can be caused by faulty timing advance, dirty carburetor jets or passageways, blocked fuel pump, a non-vented fuel supply or a non-synchronization between the carburetor and the ignition timing. The challenge when you go to troubleshoot your outboard is to systematically work your way through the variables all the while making notes on what you have tried and in what order you tried it.

Unless it is obvious what the problem is one should consider doing some of the most basic tests soon after you start to troubleshoot. One of these is to determine if fuel getting to the carburetor. If the motor starts but doesn't respond well to an increase in throttle try pumping the bulb on the fuel line and see if that makes a difference in performance. If the bulb gets relatively hard and the motor speed does not change it is likely the float(s) in the carburetor(s) are responding properly. Also make sure the gas tank is sufficiently vented. Does loosening or temporarily removing the gas tank cap make a difference? If it's appropriately vented it shouldn't. Likewise determine if the gas is fresh. Disconnect the fuel line at the fuel filter and pump the inline bulb and see if gas flows freely. If it does remove and inspect the fuel filter which may be an inline module or a filter element on the front end of the fuel pump. If it isn't it can lead to a number of performance issues created by fuel starvation.

Another common test is to use an inline spark detector to verify that the ignition system is delivering enough voltage to each plug to get a healthy spark. Inexpensive testers such as this are readily available in auto parts stores. On multi-cylinder outboard motors the motor may idle well even if one of the cylinders is not receiving a healthy spark or is not exhibiting good compression. If this is the case there may be a loss of power or inability to reach higher speeds. When one or more spark plug wires is not showing a spark the entire ignition system needs to be investigated. In recent times outboard motors manufacturers, like automobile manufacturers, have switched to solid state ignition components which may require specialized equipment to test. If the outboard ignition system is suspected it is recommended to look online at the ignition system component manufacturers web sites or the boating forums to determine what testing options are open to you. While it is tempting to buy and install new outboard electronic parts such as switchboxes this can be very expensive if you are not sure what part has failed.

An overheated outboard motor can also lead problems in a number of areas. If you suspect your outboard motor is overheating cease using the engine until track down the problem. Many outboards have telltale streams indicating the water pump is functioning properly. Cooling issues are often due to a faulty water pump impeller that is relatively easy to change. You can also attempt to flush out the cooling system. In general cooling problems due to water path blockages are harder to troubleshoot and should be left to professional outboard mechanics.

Outboard motor carburetion issues such as blocked carburetor jets or passageways are another source of performance problems. Carburetor rebuild kits can be purchased to make the job of rebuilding your carburetor easier should it be required. When disassembling and cleaning a carburetor avoid cleaning jets with rigid objects that can scratch or deform the jet. Likewise avoid overtightening needle valve screws on carburetors that employ them. Count the number of turns that a needle valve is open when you are removing it. This makes it easier to reset it when reassembling the carburetor. If there appears to be a lacquer type coating in the carburetor bowl consider taking the carburetor to an auto repair shop and having it cleaned using an ultrasonic cleaner with the appropriate cleaning solvents.

A key yet simple diagnostic test is to check the compression of each outboard motor cylinder. This requires the use of a relatively inexpensive pressure gauge that records the peak pressure reading on each cylinder. In general the pressure recorded on each cylinder should be within 10% of each other. Larger variations will often result in degraded performance and the cause should be investigated. Spraying some oil into the cylinder and repeating the test may indicate whether it is a piston ring problem. The oil may tend to temporarily seal the ring and increase the pressure reading. Scored cylinder walls, broken or seized piston rings, damaged cylinders, and blown headgaskets are among the causes of low or mismatched pressure measurements. When the cylinder head is removed pits in the top of the cylinder often indicates a broken piston ring while a very clean cylinder head and sparkplug may indicate a water leak due to a blown gasket.

During the methodical troubleshooting phases it is strongly suggested that numerous digital photographs of the details of the outboard be taken along with copious notes. What is familiar wire routing this weekend may not look so familiar when you are reattaching those wires next weekend. The results of your own testing can then be reviewed and compared with similar situations you might find on some of the outboard motor forums that can be found online. Actively posting and reading case studies on these forums is an excellent way of benefiting from the collective knowledge of others that may be faced with similar problems.

While outboard motor problems may seem daunting at first a methodical approach to troubleshooting aided by manufacturers service manuals and the experiences of others found on outboard repair forums will often lead you discovering and repairing the source of a problem.