GUIDE for inboard motor / outboard motor racing

Immerse yourself in the complexity of the problem of a boat engine racing and find out how to fix it! What could be more stressful than sailing peacefully, when suddenly your trusty boat engine starts roaring uncontrollably? It is a problem that every sailor dreads, and which raises an avalanche of questions. What is the cause? Can I repair my inboard motor myself? How to easily solve a outboard motor racing ? Fortunately, we can answer all of these questions for you. In this guide, we will discuss the symptoms, the different causes and, above all, the solutions adapted to your situation to solve this dangerous problem. Equipped with this knowledge, you will be able to take control of your rebel engine. So strap on your life jacket, grab your tool kit and get ready to dive into the (often infuriating) world of boat engine repair.

Under what conditions does the inboard motor or outboard motor race?

The following article addresses the subject of a problem frequently encountered by boat owners: an inboard engine or a outboard motor racing. But 'getting carried away' is an umbrella term that can represent a variety of situations, each with their own unique causes and solutions. Thus, we must first define the conditions that lead to this runaway. We will explore the three most common scenarios seen with inboard or outboard motors.

1. When you push the throttle, the boat motor revs.

It may happen that when you manipulate the throttle lever to accelerate, you face a boat engine racing. It spontaneously revs up but without propelling the boat. In other words, the engine seems to idle without allowing the boat to plane, despite an increase in revs. Also, it seems to only happen when trying to accelerate. The motor operates normally at low speed.

2. When you put the throttle in neutral, the rpm does not go down again.

You may also find yourself in a situation where, after placing the throttle in neutral, the engine refuses to slow down. Instead, the engine rpm persists at a high level. An inboard engine or a outboard motor racing in this way can be disconcerting but above all very dangerous.

3. As soon as you start, the boat engine revs up as it revs up

The third scenario involves the outboard or inboard engine immediately reaching its maximum rpm as soon as it is started. It's as if the engine starts with maximum acceleration, leaving no room for a gradual increase in speed.

Each of these situations presents unique challenges that require appropriate solutions. In this guide, we'll tackle these issues and help you navigate the complexities of repairing a racing inboard motor or outboard motor.

Causes of an outboard (or inboard) motor racing when you push the throttle

Problem with the positioning of your engine

When you push the throttle and your outboard motor revs but doesn't propel the boat, the positioning of the motor could be the cause of this problem. Indeed, if the engine is placed too high, the propeller can end up partially or completely out of the water when you try to accelerate. In this case, the “ventilated” propeller, that is, it spins in air rather than water, causing engine rpm to increase without effective propulsion.

Another aspect of engine positioning that can contribute to this problem is related to cavitation. Cavitation is a hydrodynamic phenomenon that occurs when the engine propeller generates vapor bubbles due to insufficient pressure. These bubbles then burst when the pressure increases, causing vibrations and disturbances in propulsion. If your engine shows signs of cavitation, it may indicate that the engine anti-cavitation plate is incorrectly positioned relative to the hull of the boat. This plate, usually located just above the propeller, helps channel water flow to the propeller and prevent cavitation. Poor positioning of this plate can therefore contribute to a outboard motor racing during acceleration.

Problem with a pitted propeller

Another thing to consider when pushing the throttle and your boat engine revs is the possibility of a pitted helix. If the positioning of the motor is correct, it is likely that the propeller hub, especially the rubber part, has come loose from the propeller itself. This is an unfortunately irreparable situation.

To clarify, the propeller is not directly attached to the motor shaft. A silent block (or anti-vibration block) serves as an intermediary. It works like a fuse in case of contact of the propeller with a rock or sand. This avoids breaking the motor shaft. This silent block can wear out over time and no longer correctly drive the propeller. It is a wear part that it is recommended to change every 4 to 5 years.

The symptoms of a pitted helix are quite characteristic: at a high speed (for example, 5000 rpm), the boat does not move forward or only slightly, whereas at a lower speed (for example, 2000 rpm), everything seems to be working normally. This is explained by the fact that at low speed, the propeller always manages to 'cling' to the motor shaft. But it 'stalls' when the shaft spins too fast...

To confirm if your propeller is pitted, you can perform a simple test. Disassemble the propeller and draw a line with a diamond pointer or a screwdriver on the end of the splined hub, on the vulcanization and on the outer hub of the propeller. Raise the propeller and cruise until you notice the outboard or inboard motor racing. Disassemble the propeller again and check if the lines you have drawn are still aligned. If they are not, it confirms that the propeller is pitted.

Solutions for an outboard (or inboard) engine that races when you push the throttle

Solution to solve the bad positioning of your motor

There are several approaches you can take to solve the overspeeding problem associated with an improperly positioned outboard motor.

The first is to adjust the position of the motor so that the propeller is not ventilated. The second solution is to change the setting of the anti-cavitation plate. These modifications will maintain efficient propulsion and avoid engine racing.

For more information on these two crucial aspects, we invite you to consult our articles dedicated to these subjects:

• Cavitating outboard motor: causes and solutions
• Outboard motor that vents: causes and solutions

Solution to solve a pitted propeller problem

Si your engine propeller is pitted, here is the procedure to follow to solve this problem:

• First, start by removing the pin on the axle and unscrewing the nut while holding the propeller or blocking it with a piece of wood.
• The challenge when the core is faulty is that you will have trouble locking the shaft because the propeller will be stuck with the piece of wood but the shaft will continue to spin. This is clear evidence of pitting! To remedy this, shift into forward gear, but take care to remove the front spark plugs to avoid any accidental and potentially dangerous starting.
• Before unscrewing the nut, be sure to check the direction of the thread so as not to tighten it further, believing that you are unscrewing it. Indeed, the step can be clockwise or anti-clockwise.
• Once the nut has been unscrewed, you should know that the propeller is mounted on the axle using splines. You may have trouble removing it. In this case, tap lightly on it with the piece of wood to mobilize it and make it slide.
• After removing the defective propeller, replace it with a new propeller that you can find used on platforms like eBay.
• Once the new propeller is in place, reassemble the assembly, making sure to tighten the nut well and replace the pin on the shaft. You will then have repaired your inboard motor or outboard motor racing when pushing the throttle.

Causes of an outboard (or inboard) motor racing when you put the throttle in neutral

Oil level problem too high

One of the possible causes of a boat engine racing when you put the throttle in neutral could be too high oil level. An excess of oil can in fact cause the engine to self-feed, which can then go into overspeed.

This situation occurs when the mixture in the combustion chamber is too rich. This results in self-powering of the motor. Consequently the rotational speed of the engine increases even in neutral. It is therefore essential to check and maintain proper oil level for optimal operation of your boat engine.

Cable problem on the throttle control

Another possible cause of a inboard motor or outboard motor racing when you put the throttle in neutral could be a problem with the throttle control cable. This cable could be seized. That is, it doesn't move as freely as it should. In other cases it is a rod which could be blocked, preventing the adequate movement. On some engines, it is a spring which helps return the throttle to its original position. This return spring could be damaged, broken or mismatched.

It is therefore crucial to check that the throttle control cable correctly returns to its stop when shifting into neutral. The movement of the cable, link and/or return spring must be checked.

To do this, remove the plate located just behind the injection pump. It gives access to the injection rail. Here, you can see the return spring and the ball joint that fits into the ramp. This makes it easy to check if the system is working properly.

Solutions for an outboard (or inboard) motor that races when you put the throttle in neutral

Solution to solve a too high oil level problem

If you suspect a oil level too high as the cause of the problem, the solution is to remove a certain amount of oil from the system. This operation is quite simple to perform:

• Locate the oil drain plug. The latter is usually located at the bottom of the engine block. Make sure you have a suitable container to catch the oil underneath.
• Remove the drain plug using a suitable wrench. The oil will begin to flow into the container. Allow sufficient time for excess oil to be removed.
• Replace the drain plug and tighten it securely.
• Next, check the oil level using the dipstick to make sure that the oil level is now correct.
• Remember, when handling used oil, to dispose of it responsibly. Used oil must be recycled and must never be discharged into nature or the sewer.

Solution for a problem with the throttle cable

If your inboard or outboard motor is racing, your throttle cable, tie rod or return spring may be damaged. In this case, you will need to replace them.

To do this, detach them from the throttle control. Take your new cable, link or return spring and insert them following the same path as the damaged components. Once in place, reconnect them to the throttle control lever.

Be sure to choose components that fit your system throttle control to avoid further problems in the future.

Causes of an outboard motor that revs (or inboard) as soon as you start

throttle valve problem

One of the possible causes of a inboard motor or outboard motor racing possibly related to a throttle valve issue. The throttle valves are the elements within the carburetors that control the flow of incoming air. Normally, when the throttle control is at idle, the carburetor butterflies should return to a closed or near-closed position.

However, if these throttles are stuck in the open or half-open position due to seizing, it can lead to excessive airflow. And this even when the throttle control is idling! As all carburetors are mechanically interconnected, if one throttle is stuck it affects the entire system. Consequently, this leads to an automatic increase in engine speed upon starting. Which explains why your boat engine is racing…

It is therefore necessary to remove the air box from the carburettors and check that the carburettors return to the "closed throttle" position when the throttle control lever is in the idle position.

Solutions for an outboard motor that races (or inboard) as soon as you start

Solution to solve a problem related to throttle butterflies

If your inboard or outboard motor races immediately after starting, you should unstick the throttle valve(s) which remain open. To do this, follow these instructions:

• First of all, it is necessary to separate the carburetors. To do this, you will need to remove the link rod that connects the throttle valve flaps. This can usually be done simply by inserting a screwdriver between the black plastic swivel and the carburetor. This should release the binding.

• Once you have done this you need to check if all the throttle flaps move freely when isolated. It is crucial that all throttle valve shafts are completely free for proper engine operation.

• If a throttle valve flap is stuck, you can use a lubricant like WD 40 to unblock it.

• If that isn't enough to unblock the damper, it's likely that there is a significant buildup of oxidation. In this case, you will have to disassemble the carburettor, remove the butterfly and its axis, and carefully clean these parts before replacing them. lubricate with WD40.

• After carefully applying the WD40 and checked that all throttles are free, everything should be back to normal. Your boat engine should no longer race on startup.

Conclusion: an inboard engine or outboard engine that races can be repaired

Solve a problem of inboard motor or outboard motor racing may seem complex, but with the right diagnosis, it is quite manageable. Whether the boat engine is racing when increasing speed, in neutral or when starting, the identification of the exact cause (engine position, pitted propeller, too high oil level, control cable faulty throttle or blocked throttle flaps) is crucial for applying the correct solution. Regular maintenance and checking of engine parts is essential to prevent these problems and keep your boat running smoothly. In case of persistent or complex problems, do not hesitate to consult a professional.

FAQ: I have my boat engine racing, what should I do?

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