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Engine bogging is one of the most frustrating issues that arise when operating a snowmobile. It’s also a fairly common problem, as many things can go wrong in a snowmobile’s engine that would cause it to bog down.
Here are four reasons a snowmobile bogs at full throttle:
- You need to replace your fuel filter.
- You need different fuel.
- You have a bad crank seal.
- There are problems with the spark plugs.
If your snowmobile bogs when at full throttle, keep reading. I’ll explain each of these problems in further detail and how to fix them.
Why Would a Snowmobile Bog at Full Throttle?
Snowmobiles bog at full throttle when there’s a problem with the engine, preventing it from working properly. To fix this, you may need to change the fuel filter or even the type of fuel you use. Problems with the crank seal or spark plugs could also cause bogging at full throttle.
Throttle refers to the mechanism that controls the engine operation and speed, controlling the amount of air allowed into the combustion chamber. More fuel can be burned if more air is in the combustion chamber, therefore producing more power.
Causes of a Bogging Snowmobile
Bogging occurs when an engine is loaded beyond its capabilities, which happens most often when the engine isn’t cared for properly or maintained well.
Let’s look at the common reasons a snowmobile might bog at full throttle.
1. You Need To Replace Your Fuel Filter
A fuel filter can be easy to forget about, but a good fuel filter is essential for a smooth ride on your snowmobile. If the fuel filter is bad or clogged, not enough air reaches the combustion chamber, and the engine bogs out, especially at full throttle.
If you notice your snowmobile’s engine is randomly hesitating, surging, or sputtering, especially when you’re accelerating up an incline, this is usually a sign that your fuel filter is clogged. Specifically, because it deprives the engine of the fuel it needs to accelerate properly.
Another sign you need to replace your fuel filter is if the engine is repeatedly stalling. Stalling will worsen and become more common as the clog worsens.
A clogged fuel filter also causes low fuel pressure, which can cause your engine to misfire. This causes poor mileage and rough idling.
Furthermore, a damaged or failed fuel pump could result from a clogged fuel filter. If the filter is clogged, the right amount of fuel won’t reach the engine. When this happens, the fuel pump tries to compensate, which places too much pressure on the pump.
Here’s how to replace your snowmobile’s fuel filter:
- Locate the filter. Your snowmobile’s fuel filter location depends on the model and engine size. The best way to find your filter is to locate the fuel injector rail near the engine and follow the fuel supply line to the filter.
- Remove the parts that block the filter. You’ll need to remove the airbox, the clutch guard cover, and some screws to access the filter. You may also need to reposition your oil tank depending on the model of your snowmobile.
- Remove the filter. Press a fuel-line removal tool into the connector until the hose unhooks from the fuel tank. Wrap a rag around the end of the hose to contain any fuel leakage. Then, do the same thing to the other connector, remove the filter, and dispose of it.
- Install your new filter. You’ll need to connect your new filter to the fuel supply line to get your snowmobile up and moving again.
- Check your work. Make sure that your fuel line is routed correctly. Then, reinstall any parts you removed to access the filter. Test run your sled to ensure you did everything correctly.
I like this Orion Motor Tech Master Quick Disconnect Tool Set from Amazon for fuel filter removals because it comes with a fuel line removal tool. It’s suitable for various vehicles, so you aren’t limited to only using it on your snowmobile.
It’s important to remember that fuel and oil filters can’t just be thrown away. They have to be properly drained and recycled according to your town’s laws. This is because fuel is easily set afire, so proper disposal is important.
In general, fuel should be drained out of the filter into a separate container with a tight-fitting lid and then sent to a sanitary landfill. Whatever you do, avoid placing the fuel into the garbage, as this could cause a chemical reaction leading to smoke or even fire.
2. You Need Different Fuel
Most modern snowmobiles can run on 87 octane gasoline blends, but some older models need premium, 92 octane fuel. If your engine is bogging out, it’s possible that you need to change the kind of fuel you’re using.
Octane measures a fuel’s detonation resistance, and if this isn’t kept under control, your engine will suffer, and bogging issues may arise.
Normal heptane, with a zero octane rating, is the worst fuel you can use in your snowmobile, so if for some reason you have that, this is almost certainly causing any problems you’re having with your snowmobile, including bogging.
Some brands, like Polaris, recommend using 91 octane fuel or higher without ethanol for the best results. If you own one of these models, using 87 octane fuel is acceptable, but your engine won’t run as well. In general, it’s best to avoid using fuel with more than 10 percent ethanol.
When buying fuel for your snowmobile, be sure to follow the owner’s manual suggestions. If you’re forced to use 87 octane fuel, try to avoid going full throttle and run the sled at slower speeds until you’re able to get 91 octane fuel. Doing this will keep cylinder pressures down, reducing the damage your engine suffers.
3. You Have a Bad Crank Seal
When a crank seal fails or is damaged, air enters the crankcase and dilutes the air to fuel ratio, leading to bogging or engine failure in extreme cases.
The crankshaft seal is located on the front of the engine and seals the end of the crankshaft. It keeps the oil that the crankshaft uses from leaking out. If you’re noticing oil leakage in addition to engine bogging, this is most likely the issue.
The most common reason for crank seal failure is general wear and tear, so if your snowmobile is old or you’ve put a lot of miles on it, there’s a chance the crank seal will become worn and damaged.
Another cause of crank seal failure is that the engine is too full of oil. If there’s not enough space for the oil, it’ll leak out the seal.
There’s also a chance your crank seal was not applied properly, which would lead to leaks and limit your engine’s ability to function properly.
Replacing a crank seal is a relatively complicated process, so it’s best to bring your snowmobile to a mechanic to have them look at it. If you want to give it a try yourself, this video may be helpful:
4. There Are Problems With the Spark Plugs
Using a spark plug that isn’t recommended for your specific model and brand of snowmobile could cause runnability problems and bogging. Furthermore, many snowmobile ignition systems are sequential, so the MAG and PTO spark plug leads, and caps have to be on the right spark plug, or the engine will have problems.
The MAG and PTO bands should be labeled with a band or some other indicator, but if they’re not, know that the MAG is the recoil side, located to the right if you’re sitting in the snowmobile. The PTO is on the left side, the clutch side.
Spark plugs ignite the mixture of air and fuel within the engine’s cylinders and are a vital part of your snowmobile’s ignition system. Some symptoms of failing spark plugs include:
- Difficulty starting your snowmobile
- Consistent engine misfiring
- Engine surging
- Bad fuel efficiency
- Difficulty accelerating
You can test your spark plugs to see if they are the issue. To do this, remove the plugs and ground them on a head bolt and turn over the engine. If a spark is visible, your spark plugs are in good condition. However, if you don’t see a spark or the spark is weak, there’s a good chance you need to replace your spark plugs.
- Family Handyman: 5 Signs Your Fuel Filter Needs Replacing
- SR&R Environmental: Fuel Filter Recycling and Disposal
- SnowGoer: How to Replace Polaris Cleanfire Fuel Filter
- Polaris SNowmobile Help Center: Engine Bog Troubleshooting
- SnowGoer: Fuel Octane and How It Affects Snowmobiles
- Snowmobile Forum: Crank Seals?
- Your Mechanic: How to Replace a Crankshaft Seal
- Wilco Motosave: Tell-Tale Signs Your Spark Plugs Are Failing
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