Starting A Boat With A 90 Hp Johnson: Easy Guide

The Johnson 90 HP engine is a popular choice for boat enthusiasts, but starting this engine can be challenging, especially for first-time users. Various factors, such as engine type, fuel consumption, and maintenance history, can influence the starting procedure and overall performance. In this discussion, we will delve into the intricacies of starting the Johnson 90 HP engine, exploring potential challenges and offering practical solutions to ensure a smooth and safe boating experience.

Check the engine is running at 100%

To check that your 90 HP Johnson boat engine is running at 100%, you'll need to perform some routine checks and maintenance.

Firstly, it's important to check the engine's compression. This is a good indicator of the overall health of your engine, and a compression test will help you identify any issues with the piston rings, which are known to be a common problem in these engines. A healthy engine should have consistent compression across all cylinders.

Next, inspect the water pump and impeller. These are crucial for keeping the engine cool and preventing overheating. Ensure the water pump has been recently serviced and the impeller is in good condition and replaced if necessary.

The fuel system also requires regular attention. Check the fuel filter and ensure it is clean and free of debris. If the engine is struggling to draw fuel, it may be necessary to manually operate the fuel pump to assist. Additionally, check the fuel lines for any signs of cracks or leaks, and ensure the fuel tank is adequately filled with fresh fuel.

The spark plugs are another key component. Ensure these are clean and replace them if necessary. Check the engine timing with a timing light to ensure the spark plugs are firing at the correct time.

Finally, pay attention to the engine's performance. If it is struggling to reach maximum RPM, it may be a sign of an issue. A healthy 90 HP Johnson engine should be able to reach approximately 5000-5500 RPM, and this should correspond to a speed of around 35-40 mph. If the engine is struggling to reach these figures, it may indicate a problem with the propeller pitch, engine trim, or a more serious mechanical issue.

By regularly performing these checks and maintenance tasks, you can help ensure your 90 HP Johnson boat engine is running at its full potential.

Confirm the RPM

Confirming the RPM is a crucial step in ensuring your 90 HP Johnson boat engine is performing optimally. Here are some detailed instructions and considerations to help you through the process:

Firstly, it's important to understand that RPM, or revolutions per minute, is a measure of how fast the engine is running. For a 90 HP Johnson engine, the dealer-specified RPM is typically around 5500. However, this can vary slightly depending on the year and model of your engine. For example, users of the 1989 Johnson 90 HP model have reported RPMs of 4000, while others have achieved RPMs of 5000-5500 with the same engine.

To confirm the RPM of your engine, start by locating the tachometer, often referred to as the "tach". This instrument measures and displays the engine's RPM in real time. It is usually located near the steering wheel or in the dashboard instrument cluster. If you're having trouble locating it, refer to your boat's user manual. Once you've found the tach, observe the needle or digital display to get an initial reading of the engine's RPM.

Next, you'll want to ensure the engine is running at its full potential. Consider factors such as engine compression, spark, and timing. A compression test will help identify any issues with the piston rings, which are known to cause problems in some Johnson engines. Check the spark plugs and ignition system for any signs of wear or damage, as these can impact the engine's performance. Additionally, inspect the camshaft and its components, including the cam follower or roller, for any damage or debris that may affect timing.

After addressing these factors, take your boat out on the water and run it at full throttle. Observe the tachometer to confirm the RPM. If the RPM is lower than expected, you may need to consider adjusting the propeller pitch. Less pitch will increase the RPM, but this should be a last resort after all other factors have been optimised.

Finally, it's important to consult your owner's manual for the specific RPM range provided by the manufacturer. This will give you an accurate understanding of the expected RPM for your particular engine model. By following these steps, you can effectively confirm the RPM of your 90 HP Johnson boat engine and ensure it's performing as it should.

Check the elevation

Checking the elevation is crucial when starting a boat, especially if you're operating a 90 HP Johnson engine at high altitudes. Here are some detailed instructions and considerations regarding elevation checks:

Understanding the Impact of Elevation:

• Engine performance can be significantly affected by altitude due to changes in air density. As you go higher, the air becomes thinner, reducing the amount of oxygen available for combustion. This can result in decreased engine power and performance.
• The 90 HP Johnson outboard motor may be designed for use at specific altitudes. Ensure you have the appropriate model for your boating location.

Checklists for Elevation Checks:

• Determine Your Altitude: Begin by finding out your current elevation above sea level. You can use a topographic map, a GPS device, or online tools to determine your precise elevation. This information is crucial for making any necessary adjustments.
• Consult the Owner's Manual: Refer to the 90 HP Johnson outboard motor's owner's manual or service handbook. It should provide specific guidelines and recommendations for operating the engine at various altitudes. There may be charts or graphs indicating required adjustments based on elevation.
• Adjust Carburetor Settings: If your engine has a carburetor, you may need to adjust the fuel-air mixture. At higher altitudes, the engine will require a richer mixture (more fuel) to compensate for the thinner air. This adjustment can be made by turning the mixture screw on the carburetor, following the manufacturer's instructions.
• Consider High-Altitude Kits: Some engine manufacturers offer high-altitude kits or modifications specifically designed for operating at higher elevations. These kits may include components such as jets, needles, or carburetors calibrated for optimal performance at higher altitudes. Check with your local dealer or authorized service center to see if such kits are available for your 90 HP Johnson engine.
• Fuel and Spark Plug Adjustments: In addition to carburetor adjustments, you may need to make changes to the fuel system and spark plugs. High-altitude operation may require a slower-burning fuel with a lower octane rating. Additionally, you might need to adjust the spark plug gap to ensure optimal combustion. Again, refer to the owner's manual or seek advice from a qualified marine mechanic.
• Regular Maintenance: Regardless of elevation, regular maintenance of your 90 HP Johnson engine is essential. This includes tasks such as changing the engine oil, inspecting and replacing spark plugs and fuel filters, and checking the propeller for any damage or debris. Proper maintenance will help ensure reliable performance at any altitude.

Remember, elevation can have a significant impact on engine performance, and it's crucial to make any necessary adjustments to ensure safe and efficient operation of your 90 HP Johnson outboard motor. Always refer to the manufacturer's guidelines and consult with marine professionals if you have any questions or concerns.

Check the engine has enough compression

Checking the engine has enough compression is a vital step in ensuring your boat's engine is in good condition. Here's a detailed guide on how to do this for your 90 hp Johnson engine:

Step 1: Understand the Engine's Requirements

Before beginning, it's important to consult your engine's manual to understand its specific requirements. The process may vary depending on factors such as the number of strokes, fuel injection, and the presence of onboard computers. For example, if your engine is hand-cranked or has a starter motor, the steps may differ.

Step 2: Prepare the Engine

Ensure the engine is warm, as this provides more accurate and relevant readings. Run the engine until it reaches its normal operating temperature. This is important because a cold engine may not provide accurate compression test results.

Step 3: Prevent Unintended Ignition

Disable the ignition to prevent accidental engine start-up during the test. This can be done by pulling the engine kill switch or disconnecting the battery. If you disconnect the battery, remember to reconnect it later for cranking an electric start engine.

Step 4: Remove and Inspect Spark Plugs

Remove all spark plugs, numbering the leads to ensure proper replacement later. Inspect the spark plugs for any damage. The electrodes should have the correct gap, and their colour should be a medium tan to brown after high-speed operation, or dark brown to black after idling at slow speeds. Lighter colours indicate a lean mixture, which means there is not enough fuel, and the engine should be checked to prevent damage.

Step 5: Adjust the Throttle

Move the throttle forward to facilitate air entering the cylinder as you crank the engine. However, if you have an electric start engine, you may need to consult your owner's manual, as you might not be able to perform this step. Some engines have adequate air intake without this adjustment.

Step 6: Use a Compression Gauge

Screw a compression gauge into the first cylinder, ensuring that the plug leads are clear of the flywheel and any moving parts. Crank the engine through at least four or five flywheel revolutions, or until the compression gauge needle stops advancing. The engine won't start as the plugs have been removed, but there may be fuel injected into the cylinder, so be cautious of any sparks or smoking.

Step 7: Record Readings and Repeat

Note the reading for the first cylinder and repeat the process for each cylinder, recording the results.

Step 8: Interpret the Results

Compare your readings to the expected compression values for your engine type. For a 90 hp Johnson engine, the expected compression values may depend on the year and model of your engine. Generally, two-stroke engines should have compression readings of around 110-130 PSI, while four-stroke engines should be in the range of 180-210 PSI. If your readings are low or erratic, further investigation or professional assistance may be required.

Remember, this is a general guide, and the specific steps may vary depending on your engine's unique characteristics. Always refer to your engine's manual and seek professional advice if needed.

Check the spark and fuel

To check the spark and fuel of your 90 HP Johnson boat, you can perform the following steps:

Checking the Spark

• Remove all spark plugs.
• Use a spark tester to check for a strong blue lightning-like flame. The spark should jump a 7/16" gap with a snap.
• Perform this test when the engine is cold and hot if possible, but it is not necessary.
• Ensure the gap is set to 7/16" as this is important for accurate testing.

Checking the Fuel

• Check that fuel is good and flowing properly.
• Have someone pump the fuel primer bulb constantly to force fuel through the engine's fuel pump.
• If the engine was running fine before but now struggles to start, it could be due to the ethanol evaporating from motor heat.

Additional Tips

• Perform a compression test to ensure the engine is running close to 100%.
• Check the engine's rpm and ensure it is at the correct level for your boat and engine type.
• Check the elevation you are at and ensure the prop is correct for your boat.
• Keep the hull clean and ensure the trim is good.
• A lower pitch will increase rpms.

By following these steps and tips, you can effectively check the spark and fuel of your 90 HP Johnson boat and identify any potential issues.

Frequently asked questions