Troubleshooting Guide: Boat Dies When Put In Gear

If your boat dies when you put it in gear, it can be due to a variety of issues. A boat may quit after putting in gear due to a bad fuel pump, low idle, bad shift cable, bad spark plugs, fuel shortage, and other reasons. A low idle is one of the main problems that will cause a boat to abruptly stop when it is put into gear. If your boat doesn’t have enough power, it’ll idle at a lower and lower speed. Eventually, the engine will lose power and quit. A bad shift cable may also be the culprit, causing the momentary shift interrupter switch to engage and kill the engine.

Low idle speed

A low idle speed can cause a boat to abruptly stop when put into gear. If your boat doesn't have enough power, it will idle at a lower and lower speed until the engine eventually loses power and quits.

There is back pressure on the motor exhaust when submerged underwater, which restricts airflow through the motor and causes it to idle slower than on land. Therefore, the final tuning should be done on the water, not on a driveway. The idle in neutral should be around 800 RPM, and around 600 RPM in gear.

If your boat is idling at a low speed, it could be due to a dirty carburetor. If your carburetor is covered in a layer of dust or grime, give it a good, thorough cleaning. If you clean it and the carburetor still won't cooperate, you may need to take it to a repair shop.

Another potential cause of low idle speed is a bad interrupt switch. An interrupt switch is a device that allows you to switch gears with ease. If it has become disconnected, that could be why your boat is shutting down when you try to shift into gear. If you observe that the switch is bent, broken, disconnected, or disabled in any way, it will need to be fixed or replaced. While you could try to tackle this problem on your own, a broken interrupt switch can be tricky, so it might be wiser to involve a professional repairer.

Faulty fuel pump or filter

A faulty fuel pump or filter can cause several issues with your boat engine. Here are some detailed symptoms of a faulty fuel pump or filter and some direct and instructive steps to help diagnose and address the problem:

Symptoms of a Faulty Fuel Pump or Filter:

• Engine Sputtering: If your engine sputters at high speeds or while starting, it could be due to a problem with the fuel system, including the pump, filter, or injectors. A clogged fuel filter or fuel lines, or a faulty fuel pump, can cause the engine to sputter if it isn't getting enough fuel.
• Poor Engine Performance: A faulty fuel pump can cause the engine to hesitate, surge, or sputter under heavy loads or during acceleration in rough waters. The engine may also shake or stutter at different speeds due to insufficient fuel.
• Rough Engine Sounds (Whine): If you hear a whining sound from your fuel tank, it could indicate contaminated fuel, a damaged fuel pump, or low fuel levels. Normally, the fuel pump should make a soft humming sound.
• Increased Engine Temperatures: A faulty fuel pump may cause the engine to overheat due to insufficient fuel supply, leading to a continuous rise in engine temperature.
• Decreased Fuel Gauge Values: If your pressure gauge shows that less fuel is being supplied than what's required by the manufacturer's specifications, it could be a sign of a faulty fuel pump.
• Increased Fuel Consumption: If you find yourself filling up your boat more often, it could be due to a faulty fuel pump sending too much or too little fuel, causing the engine to overheat or consume more fuel.

Troubleshooting and Addressing the Issue:

• Check Fuel Levels and Connections: Ensure that you have sufficient fuel in the tank and inspect the fuel connections and hoses for any leaks or kinks. Also, check the fuel filter for clogs or degradation, and clean or replace it if necessary.
• Test Fuel Flow: Establish if there is a continuous flow of fuel from the tank to the pump. Pump the primer bulb and ensure that fuel travels to the outboard fuel filter, indicating uninterrupted flow.
• Listen for Pump Priming: If your boat doesn't start, listen for the fuel pump priming. In a dual-pump system, both pumps will prime with a whirring sound. If you don't hear this sound, it could indicate a faulty fuel pump.
• Inspect the Diaphragm: The diaphragm is a rubber component inside the fuel pump that pushes the fuel through. Look for signs of damage, such as stalling, leaking, or fuel escaping into the water.
• Maintain Your Fuel System: Regular maintenance can help prevent issues with your fuel pump and other components. Use fuel stabilizers, monitor and replace fuel filters regularly, and inspect and tighten fuel lines and hose clamps.

Faulty spark plugs

Spark plugs are a critical component of your boat's engine. They take in high-voltage electricity at one end and ignite a spark at the other, firing the air-fuel mixture in the engine cylinders to create the combustion that powers your boat. When spark plugs begin to fail, you may experience issues such as engine misfires, difficulty starting the engine, and decreased acceleration.

Engine Misfires

Engine misfires are one of the most common signs of faulty spark plugs. If your boat's engine stumbles, hesitates, or experiences a rough idle, it's likely that one or more spark plugs aren't firing correctly. Misfires often become more noticeable during acceleration, affecting your boat's overall performance.

Starting Issues

Another indicator of potential spark plug issues is difficulty starting your engine. If your motor takes longer than usual to crank or requires multiple attempts to start, it could mean that the spark plugs aren't generating a strong enough spark. This is especially important during cold starts when a reliable ignition is crucial.

Decreased Acceleration

If your boat experiences decreased acceleration, it means the engine isn't producing enough power. This is one of the most obvious signs of a spark plug issue. However, it could also indicate a larger mechanical failure, so further diagnostics may be necessary.

Loss of Engine Power

A loss of engine power could be due to faulty spark plugs. Without a spark, the engine cannot run. So, if your engine loses power or won't start, checking the spark plugs should be a priority.

Physical Inspection

You can also examine the spark plugs for damage or fouling. Check the insulator tip, boot, and upper and lower insulators for any signs of damage. A normal spark plug will appear dry and have a grayish colour. Deviations from this, such as a wet plug or a plug covered in soot, can indicate issues such as water in the fuel or too much oil in the fuel.

If you suspect faulty spark plugs, it is recommended to consult a professional for further diagnosis and repair. They can help identify and resolve any spark plug issues, ensuring your boat's engine performs reliably.

Transmission issues

If your boat motor dies when you put it in gear, it could be due to a number of issues with the transmission. Here are some possible causes and solutions:

Low Idle Speed

A low idle speed is one of the main reasons a boat motor dies when put in gear. When a boat doesn't have enough power, it idles at a lower and lower speed until the engine eventually loses power and quits. This can be caused by back pressure on the motor exhaust when submerged underwater, which restricts airflow and causes the motor to idle slower. To fix this, set the idle with the motor in the water, ensuring the RPMs are high enough to keep the engine running. The idle in neutral should be around 800, and around 600 in gear.

Bad Shift Cable

A bad shift cable can cause issues with shifting gears, making it difficult or impossible to shift into gear. This could be due to a stiff cable, which can also cause the momentary shift interrupter switch to engage and kill the engine. To fix this, the cable may need to be replaced.

Interrupt Switch Issues

An interrupt switch is a device that allows you to switch gears easily. If it becomes disconnected or damaged, it could cause the boat to shut down when shifting into gear. Inspect the interrupt switch and if it appears to be bent, broken, disconnected, or disabled, it will need to be fixed or replaced. This may require the assistance of a professional repairer.

Low Engine RPMs

When a boat engine is in gear, the RPMs drop. If they drop too low, the engine can die. This can be caused by faulty cylinders that are not firing correctly. Ensure that the engine is viable by performing a compression test, which will confirm that the engine is not getting ready to blow up and that there are no bad cylinders causing the issue.

Fuel and Carburetor Issues

Fuel and carburetor issues are a common cause of boat motor issues when put in gear. If the carburetor is dirty or clogged, it can cause the motor to stall. Check the fuel lines, fuel filters, and fuel tank for any blockages or debris, and ensure that the carburetor is clean. Regular engine maintenance can help prevent stalling and other engine problems.

Carburetor issues

A bad carburetor can also cause the engine to stall after reaching certain RPMs. If your carburetor is covered in a layer of dust or grime, it needs to be cleaned. A thorough cleaning should solve the problem. If cleaning doesn't work, you may need to take it to a repair shop to get it fixed.

To avoid carburetor issues, regular engine maintenance is essential. This includes checking and cleaning or replacing the fuel filter, as well as ensuring the fuel pump is functioning properly.

Frequently asked questions