How to Troubleshoot Johnson Boat Motors

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It's frustrating to launch your boat and realize the motor won't start. If you own a Johnson boat motor, it's going to have the same problems as any other gasoline-powered motor. If you decide to troubleshoot the problem yourself, you'll need to understand some basic concepts on what makes the engine run.

There are three elements required for your Johnson engine to run properly: compression, fuel and fire. If any of these elements are out of sync, your engine won't run properly--if it even runs at all. It would help to buy a handbook about your particular engine before you start troubleshooting.

Items you will need

  • Johnson manual for your particular motor

  • Compression gauge

  • Leakdown tester

Check for simple problems that may cause the engine to run poorly. If your engine isn't starting, check for a loose spark plug wire. Something as simple as a wire not connected properly can keep your engine from firing. Also, check to make sure the battery cables are connected properly and working to full capacity. Simple and relatively inexpensive problems like this will make your motor not run.

Make sure a fuel problem isn't the culprit. Fuel problems can sometimes be mistaken for ignition problems. Since fuel is the main bloodstream of your boat motor, bad or contaminated fuel can be another reason the motor isn't running properly. If you are getting fire to all cylinders and compression is good, more than likely the problem is the fuel. Many things can cause a fuel problem--bad gas, a bad fuel pump, loose fuel line, clogged carbs, or the fuel tank isn't venting correctly. Be sure to check out all of these basic problems before buying new parts. Parts replacement can be a timely and expensive purchase when dealing with any boat motor.

Troubleshoot the ignition. This is where you might need to call for experienced help. Check the timing to make sure it's functioning fully. The problem could be as simple as a broken bare wire or something shorted out. If the problem seems more serious, take your motor to a licensed Johnson technician. Repairing ignitions can be a timely and costly expense. Since you most likely will not get a refund on parts you've purchased, the repair needs to be done correctly the first time.

Run a compression test. This will more than likely tell you if there are problems with the internal structure of your engine. You might have damaged cylinders, stuck rings due to a buildup of carbons or other major problems. Also, perform a leakdown test on the cylinders to see whether leakage is occurring due to wear, stuck or damaged rings. If the leakdown test shows there's more than 15 lbs. difference on any of the cylinders, stop running the motor and get it fixed. You could end up with more problems than you started with.

Be sure you're mixing the proper grade of fuel and oil as recommended by your Johnson dealer. Using an inappropriate mix of fuel and oil is a sure way to ruin the internal workings of your engine.

Check the cooling system. Nothing will destroy your boat's engine quicker than a few moments of overheating. It's advised to replace the water pump impeller every other season. Non-use is the worst abuse, and the impeller can dry rot and go bad.

Take the boat to a licensed Johnson boat motor technician if you've tested the engine and all other components. Boat motors can become a money pit if not maintained and repaired properly.


  • Be careful when dealing with gasoline or moving parts of an engine.


  • Non-use is more destructive to a boat motor than overuse. Add a fuel conditioner to your fuel tank and let it run before storing your engine for a long period.
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