Your snowmobile keeps fouling plugs because of excessive idling, low-speed driving over a long distance, carburetor issues, worn piston rings, blocked air filter, rand too much gas. Riding the snowmobile for short periods and flooding from the engine failing to start will cause the plugs to foul. 

When your snowmobile has been running well, and then it suddenly starts to sputter and die, the plugs are most likely the problem. Fouling plugs occur in all automobiles, but they’re more common in two-stroke older model snowmobiles. 

Your snowmobile is fouling plugs usually due to mechanical issues. However, many people may unknowingly be causing the plugs to foul. The rest of the article will discuss the causes of plugs fouling and the measures you can take to minimize it. 

Why Do Snowmobiles Foul Plugs?

It’s frustrating when your snowmobile keeps failing to start or sputters every morning. Half the time, when you try to find the cause, you have fouled plugs. You can’t just keep replacing spark plugs without finding the root cause. 

Snowmobiles foul plugs because of a dirty carburetor, blocked air filter, worn piston rings, or too much gas. Idling the snowmobile for too long, riding for short distances

, incorrect heat range, or riding long distances at slow speeds can foul plugs. Plugs also foul due to engine overheating. 

Fouling plugs can leave you snowed in or stuck when you need to use your snowmobile. Unfortunately, the spark plugs may foul at any time. You can prevent the inconvenience by checking and servicing your snowmobile regularly. You also need to avoid idling the engine for too long. 

This video discusses some of the possible causes of fouling plugs in snowmobiles.

How To Tell If Your Plugs Are Fouled

Snowmobiles are prone to fouling plugs because you may be forced to ride slowly over a long distance due to the snow. You’re also not burning gas and oil fast enough, and the cold engine doesn’t help matters, as you may be tempted to idle it for long when attempting to warm it. All of these instances can cause plugs to foul. 

When your snowmobile starts to sputter, and the engine fails to start, you need to check the plugs. You are likely to discover any of the following conditions:

  • A normal spark plug. This will have brown or grayish deposits on the electrodes. Since the plugs are not the problem, you need to determine what is wrong with your snowmobile.
  • Oil deposits. Black, oily deposits are a sign of an oil-fouled plug. The oil may have leaked through worn pistons or valves into the cylinders.
  • Burned plugs. You’ll know the plugs are burnt when you see melted electrodes, blisters on the insulator, or white deposits. 
  • Wetness on the plug. Engine flooding may cause the plugs to get wet. This usually occurs when you attempt to start the engine multiple times with no response. 
  • Broken electrodes. Flattened or broken electrodes signify the use of the wrong plugs. A plug that is too long will damage the engine, while plugs that are too short will cause spark plug fouling.
  • Worn or eroded electrodes. Plugs that have been in use for too long eventually wear out and need to be replaced.
  • Carbon fouled. When you find dry, black soot on the electrodes, the plugs are carbon fouled. 

Remove plugs from your snowmobile to find out if they are fouled. Examine the electrodes to find the cause of the fouling and solve the problem once and for all. If the plug fouling is due to worn or use of wrong plugs, you only need to replace them. 

However, If the plug has oil deposits, replacing the plugs is not enough. You need to find out the cause of the oil leak and fix it. 

How To Fix Fouled Plugs

When you remove the plugs in your snowmobile and discover the fouled plugs, how you fix the problem will depend on the cause and the type of plug fouling. 

Your Snowmobile Has Carbon Fouled Plugs

If your snowmobile has carbon fouled plugs, you need to replace them. However, you should consider using a “hotter” spark plug. The higher the number, the hotter the plug. Hotter spark plugs retain more heat at the tip, allowing for an easier burn of carbon deposits and preventing premature fouling. 

Your Snowmobile’s Fouled Plugs With Oil Deposits Are Ruined 

If the snowmobiles fouled plugs with oil deposits are ruined, you should  find the cause of the oil leak to keep it from recurring. If the valves or pistons are worn, you need to replace them to keep the plugs of the snowmobile from fouling constantly. 

Your Snowmobile Has Wet Spark Plugs

If your snowmobile has wet spark plugs, you should wipe them off. Wet spark plugs are a common problem due to engine flooding, typically when you try to start the engine multiple times. However, instead of wiping them, you can also just wait for them to dry before reusing them. 

Your Snowmobile Has Burned Plugs 

If your snowmobile has burned plugs, you need to replace them. Burned plugs are easy to spot, and a common reason for why snowmobiles fail to start. While replacing them, you should find out why your engine is overheating. It’s essential to get plugs with the right heat range.

Your Snowmobile Has Worn Plugs Or Broken Electrodes 

People who haven’t replaced their plugs on their snowmobile regularly will usually see worn plugs or broken electrodes. Plugs will eventually wear down like all things and need to be replaced. Therefore, it’s essential to have your snowmobile serviced regularly to avoid this issue.

However, you need to ensure you follow the manufacturer’s manual on which spark plugs to use. 

These NGK Snowmobile plugs, from have ten BR8ES spark plugs in the box. The overall height is 0.31 inches (0.8mm) and they are made of nickel. They have no projection, are durable and they guarantee optimum performance.  

Effects of Fouling Spark Plugs

Your snowmobile will perform optimally when the plugs are clean and when the electrodes are not damaged. Fouled plugs affect how the engine performs.

Sometimes fouled plugs will cause stalling, but they can still run for a little longer if the damage on the plugs is not significant. 

Running your snowmobile on fouled plugs can cause several problems: 

  • You may start using more fuel to cover the same distance. 
  • The snowmobile may become sluggish.
  • The snowmobile may keep stalling and eventually stop responding when you start the engine.
  • Instead of running smoothly, the engine may keep misfiring because of interference in the combustion process. 
  • Fouled spark plugs cause the engine to produce a rough sound and vibrations, especially when idling. 

Besides the negative effect on how your snowmobile runs, fouling spark plugs will reduce your confidence in taking a long ride, especially on routes where you’re less likely to get help.

If the snowmobile was your escape and way to enjoy nature in winter, it ceases to be fun because now you have to worry about it stalling in the middle of nowhere.

How Often Should You Change Spark Plugs on a Snowmobile?

Sometimes spark plugs keep fouling because you have used them for too long. You don’t have to wait for the spark plugs to foul before you can change them, especially if you have used them for a while. Instead, you should change the spark plugs regularly for optimal snowmobile performance.

You should change spark plugs on a snowmobile every season. However, this can depend on how often you use the snowmobile. If you rarely use the snowmobile, a set of plugs may last you more than a season, while heavy use may require more spark plugs per season.

Worn spark plugs are vulnerable to fouling. They may even cause your snowmobile to stall while you are out riding, which can prove costly and uncomfortable at the peak of winter. Changing your spark plugs regularly will guarantee that your snowmobile will roar to life every time you turn the ignition.


Snowmobiles keep fouling plugs for various reasons. The conditions under which they are driven expose plugs to fouling. However, you can control how often you replace the plugs. You also need to ensure you service your snowmobile regularly so no underlying issues cause the plugs to foul.


Answers To All: How often should you change spark plugs on a snowmobile?