Mercury outboard motor, no surging here

Why Does an Outboard Motor Surge?

Engine surging is when the RPMs in an outboard engine are fluctuating up and down, sometimes wildly.

It does not sound right, and is noticeable right away. You instantly want to fix it and get it back to its proper running state right away.

With that in mind, let’s have a look at possible causes of your outboard surging and how to fix it.

Why Does an Outboard Motor Surge?

Engine surging on an outboard motor is likely due to a blocked pilot jet inside the engine. This can be removable or integrated. Clean it with the right tools and the surging should stop.

You may not need to take the carburettor out to do this, depending on how your outboard is made.

Mercury outboard motor, no surging here
My shot of a Mercury outboard motor – no surging here, fortunately!

How to Fix Engine Surging on Your Outboard

To fix engine surging on your outboard, find the pilot jet on your outboard engine, take the idle screw out with a screwdriver. Then remove the jet with needle nose pliers and clean it. If that does not work, try removing and cleaning the carburettor.

You will need the right tools to clean the pilot jet. Get A 1/1300th” wire drill bit as it is small enough to get inside the pilot jet and get it clear. Even a sewing needle or paperclip will be too big as the hole on the pilot jet is that small!

How you get to the pilot jet on your outboard motor will depend on the type of pilot jet the motor uses, with 2 main types used.

2 Types of Pilot Jet

  • Removable pilot jet
  • Integrated pilot jet

You can access the removable pilot jet, usually made of black plastic, on your outboard by removing the idle screw on the engine. This then lets you access the pilot jet to remove it for cleaning. Remove it and clean as described above with a thin wire drill bit or similar. 

Once cleaned and unblocked, put the pilot jet and idling screw back in and try it out. Hopefully, this cleaning process will fix the engine surging.

You can see a pilot jet being removed from a Honda 8HP 4-stroke outboard for cleaning to improve the idling of the motor in the video below.

The integrated/internal pilot jet is more difficult to get at because it involves taking off the carburettor first and then getting to the outboard engine’s pilot jet.

To do this, remove the carburettor to get access, as with the removable pilot jet, remove the idling screw. From there you should then have access to the pilot jet on your outboard. You will then need to insert your cleaning instrument and clean the pilot jet directly in the engine.

Removing the Safety Cap to Get Access to the Pilot Jet on an Outboard Motor

If you’re having trouble accessing the pilot jet on your outboard and you are sure you want to fix it yourself, you can remove the safety cap that might be there to prevent you accessing it and modifying the screw.

YouTuber ‘That Boat Guy’ shows that drilling a small hole in the brass safety cap allows you to remove the safety cap with another instrument like a screwdriver at an angle, or perhaps a hook or some wire.

Once the cap is off, you can adjust the pilot jet air mixture screw with a flathead screwdriver and adjust this until you get a smooth idling outboard motor.

Remember, if you find this difficult or daunting, you can always take it to an outboard mechanic who can help you with it.

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