6 reasons why Mercury Outboard Stall At Idle

Mercury outboards are a great option when searching for a high-tier engine for your boat. If you prefer performance over budget, then mercury outboards are the answer for you. But it can be very tormenting when the outboard motor doesn’t idle properly.

Things can go out of hand, especially when you try to put the machine at neutral, and it stalls whenever mooring. You must be wondering why your mercury outboard is stalling at idle. Well, there can be several reasons for that. So let’s take a look at the reason first-

Why Does The Mercury Outboard Keep Stalling At Idle?

If your boat engine keeps stalling, then there is an issue with fuel leaking. We think there are three common reasons that can be causing the problem.

One is that the engine lift pump has failed somehow, or the boat is out of fuel, or there might be a blockage or air leak in the fuel line connecting the fuel tank with the engine. In the last few years, we have seen different types of pumps from different manufacturers. So it is important to know what kind of pump you have.

why Mercury Outboard Stall At Idle
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If you have a low-pressure electric pump, troubleshooting it can be as easy as switching on the key and then waiting for the pump to activate.

6 Reasons Why My Mercury Outboard Stalls At Idle

A mercury outboard that frequently stalls while idle should be addressed and solved as soon as possible. Neglecting it will further damage the engine. So, let’s take a look at the checklist given below-

Carburettor Check

Usually, the problem lies within the carburetor, if there is an issue with the outboard stalling. If you are lucky, all you got to do is tight some screws or make some minor adjustments in the carburetor. So, better to check first and then act accordingly.

Moreover, a dirty carburetor can also cause this type of problem. Experts have stated that cleaning up the carburetor and tightening up some idling screws is enough to get the board on the run again. So, the cleaning cycle is a must for this. If you are not convenient with the cleaning, take help from the experts.

Fixing The Fuel Injectors

There might be an issue with the faulty injectors for clogging problems. If your mercury outboard has fuel injection in place of a carburetor, we suggest you clean the idle air control (IAC) valve. If you haven’t done proper maintenance and service to your unit for a long time and there is a big chance that the fuel injection has clogging issues.

Clear the IAC valve and make sure the valve is regulating the airflow into the engine like before. Make sure there is no dirt or debris and the air can pass without a blockage. You can also replace the IAC valve if necessary.

If you have an older version of mercury outboard, just dismantle the system and take it to the nearest service centre and service the fuel injection in order to clear the flow of fuel.

Replacing The Air Filter

If the airflow in the engine is interrupted, it can be a significant reason to cause a problem in the mercury 40 hp four stroke or 9.9 four strokes or any other outboard. Interrupted airflow will lead to stalling issues even though you are not putting any pressure on the system.

The common sign is that when the powerhead is not getting sufficient air or even fuel, that can cause your engine to stall, especially when at idle. So, what are you going to do when you face this problem?

Simply clean or replace the air filter of your engine. Everything will be fine if you don’t see any clogging issues with the venting system. So, solve the airflow issue, and the stalling will be fixed.

Check The Valves

When there is a damaged air valve in the system, it can create issues like stalling. Inconsistent fuel supply to the engine can lead to stalling problems. If the airflow is all good and there are no issues with the filters, you should check the valve for probable damages.

If you notice a defective valve, replacing it with a new one is the only option we could think of.

Inspecting The Spark Plugs

Take out all the spark plugs and see if those are the right ones for your outboard. Examine their gaps and check if the electrodes are in good shape. So, when you are done with the inspection, clean the plugs and reinstall them, or you can just replace them with new ones. Changing the spark plugs regularly is good for the engine since they don’t cost you much.

Don’t forget to check that the plug cables are in good condition and well connected with the plugs.

[Note: old spark plugs are often covered with oil or carbon, this could lead to several problems for the motor, like head gasket leakage or low engine compression]

Call The Manufacturer

So, even after doing everything we stated above, call the mercury support and ask them for their help if you still face the problem. A professional will easily isolate the problem, and you could also get a helping hand in troubleshooting the problem.


Question: how to adjust the idle on a mercury outboard motor?

Answer: In order to adjust the idle, get a screwdriver and insert it into the mercury’s idle adjustment screw placed in the bottom of the carburetor. Next, keep it turning to the left until the motor continues to run. Insert the driver in the valve screw and rotate it to right in 1/8- turn increments to the right till you see the motor is idle smooth and even.

Question: What RPM should an outboard idle at?

Answer: if you have a passenger car engine, the idle speed would be around 600-1000 RPM. In the case of medium and heavy-duty trucks, the RPM is like 600. For a single-cylinder motorcycle, the idle speed is approximately 1200-1500 RPM.

Final Words

If you follow the steps we have listed above appropriately, you can easily manoeuvre through the issue without a hassle. So, we hope the article will help you solve the issues with your Mercury outboard and let us know if you have any questions regarding it.

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