Why Does My 2 Stroke Have A Wet Spark Plug?

Does your 2 stroke dirt bike have a wet spark plug?

What does it mean, what caused it, and how do I fix it? All of this will be covered in this article, so keep reading…

What Is A Wet Spark Plug?

A wet spark plug is simply a spark plug with the insulator and ground electrode wet and usually black in color when removed from your dirt bike cylinder head. 

Rich jetting causes spark plug to foul
Wet fouled spark plug (maybe yours is even more wet!?)

What Happens When You Have A Wet Spark Plug?

Common symptoms are sputtering, poor performance, hard to start, or not starting at all. Your 2 stroke dirt bike could be flooded with fuel as well. 

If it gets too wet, the spark will not be able to ignite the mixture and eventually foul the plug. This results in a dirt bike that won’t run or start

Why Is It Wet?

A wet spark plug usually means that the air fuel mixture is too rich. Too much fuel (wetness) and the spark plug will foul. 

A wet fouled spark plug will generally be black as well due to the rich mixture

This can easily be caused by poor jetting, but that’s not always the case. 

Common causes of a wet 2 stroke spark plug include, but are not limited to:

  • Low compression
  • Blown head gasket
  • Incorrect fuel
  • Choke is still on
  • Engine got flooded
  • Jetting too rich

How To Fix It

So, now that you know some possible reasons why your spark plug is wet and/or fouled, it’s time to figure out how to fix it.

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Let’s look at each cause to determine what the root of your problem is. 

You must troubleshoot it so that you don’t start replacing parts without knowing where the real issue is. It’s best to do one thing at a time and test to confirm your repair. Doing this has saved me a lot of money and time in the long run. 

Low compression

Low compression means that the engine cannot compress the air and fuel mixture to properly burn it. Since it can’t be fully compressed and ignited, some of the fuel goes unburnt.

This results in excess smoke out the exhaust, a buildup of carbon on the piston and exhaust port, as well as a wet spark plug. 

Low compression is most commonly caused by a worn top-end. You can test the compression to see how it compares to stock. Further inspection must be done to determine what exactly is worn out in the top-end of the engine. 

Blown head gasket

A blown head gasket can cause a wet spark plug. Coolant may leak into the cylinder and get into the air-fuel mixture. This will cause it to run poorly and possibly sound differently. 

If your spark plug is wet, take a quick peak at the coolant level. Low coolant level may mean the head gasket is blown. 

Incorrect fuel

Using the wrong fuel or poor quality gas can cause a wet spark plug. 

Higher octane fuel, such as race gas, will run rich and make the plug wet over time if not jetted appropriately. 

Use the recommended octane for your 2 stroke by the manufacturer. Any higher does not produce more power unless the compression ratio is higher than stock. 91 octane premium pump gas is generally sufficient for most 2 stroke dirt bikes. 

Poor fuel quality will also cause problems. Gas goes bad by breaking down and absorbing moisture from the air over time. It’s best to use ethanol-free gas because it lasts longer before going bad. 

Bad gas from an infrequently used pump station can also happen. 

Choke is still on

Everyone’s done it. Did you forget to turn the choke off?

The choke allows more fuel into the mixture, which is great for starting a cold engine, but it will be too rich and run poorly once the engine is warm. 

If your spark plug is wet, take a quick check to see if your choke is off and functioning properly. 

Engine got flooded

A flooded engine will surely get the spark plug wet and often foul it. 

Engine flooding can occur from tipping your dirt bike over if it’s carbureted, taking too many kicks to start the bike, or stalling the engine when the jetting is too rich. 

To fix a flooded engine, turn off the gas, tip the bike over to let out possible excess gas, and then let it sit for at least several minutes for the gas to evaporate out. 

You will probably have to hold the throttle wide open to get it to start with a flooded engine. 

Jetting too rich

As mentioned at the beginning of this article, rich jetting will cause the spark plug to be wet and get fouled. 

It’s usually going to be the pilot jet circuit that is the cause because it controls the mixture at smaller throttle openings. 

Leaning out the air screw or pilot jet should make it run cleaner and better. 

Looking for a step-by-step guide to start jetting your 2 stroke in just a few minutes? Click here to learn more (even if you’ve never touched a carb before).

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Kelley Fager

I help newer riders learn to safely ride with confidence by teaching basic techniques in a way that's easy to understand. Learn To Ride With Control Here

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