Your snowmobiles fuel pump works a lot like a heart by pumping fuel from the tank to the engine so your sled will run. Without this relatively simple part, your gas tank would remain full, and no combustion would take place to power the machine and turn its wheels.
How does a snowmobile pump work? I will walk you through it one part at a time so you can see how it makes fuel flow.
A snowmobile fuel pump sucks gas from the tank where it is stored and moves it into your engine, where an electric spark from your spark plugs ignites it. The pump uses simple intake and output valves to quickly transfer small amounts of fuel. The pump functions continuously when turned on, even when you idle, so the engine doesn’t stop.
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How Does A Polaris Fuel Pump Work
Polaris fuel pumps have three hose tubes that lead in and out to move fuel and create suction that draws fuel into the pump.
The pump itself regulates how much fuel reaches the carburetor at a time. The process is very simple and based on the pressure created by the fuel moving around and going into the engine.
1 – Getting Pressure
The carburetor line leads into the top of the pump. As gas goes out of the carb, it creates a vacuum, which this tube transfers to the pump through suction or negative pressure.
This pressure activates the parts inside and ultimately causes the pump to draw on the inlet tube to suck gas up from the tank.
2 – Moving Fuel In
The negative pressure from the carburetor line pulls fuel into the inlet chamber of the fuel pump by causing the diaphragm to flex.
A diaphragm is a mylar sheet that moves up and down with pressure to draw fuel inward and directs the flow by blocking or uncovering the inlet and outlet check valves.
3 – Check Valves
Your check valves are small and roughly tubular, with a tiny space down the center to allow fuel to pass through.
Using two of these valves lets minuscule amounts of fuel pass through the chambers very quickly.
The speed of this movement helps it exit and reach the carburetor.
4 – Getting Gas Out
Fuel pumps use pressure and choke points to speed gasoline through chambers that exit via another tube or fuel line.
The third line goes out to your carburetor and then to your engine.
Mikuni Pulse Fuel Pump Instructions
A Mikuni pulse fuel pump is made of just a few parts. The main body is metal in three segments that form chambers inside.
Between the body parts are rubber gaskets and a thin mylar sheet known as a diaphragm because it flexes, drawing fuel in and pushing it, similar to how a human breathes from the diaphragm.
There are also small openings between the chambers with mylar nipples inside called check valves that restrict the flow of gasoline.
Other than these parts, there are tubes (hoses) and a few screws to keep the pump together in one piece.
1 – Fuel Inlet
The chambers inside a Mikuni fuel pump are all between the top, center, and bottom body pieces made of metal.
There are rubber gaskets between the metal parts and the flexible diaphragms to create a seal and prevent the metal and plastic pieces from rubbing on each other.
The fuel inlet chamber is where fuel enters from the gas tank drawn in through a hose using negative pressure to pump or pulse a few drops at a time.
A third tube from the carburetor creates negative pressure as fuel leaves, creating a vacuum.
2 – Moving Gas Through
The mylar diaphragms inside a Mikuni pulse fuel pump flex downward from the negative pressure, moving gas through the chamber.
The diaphragms also control the flow through mylar inlet and outlet check valves.
First, the outlet is closed, and the inlet opens to draw fuel inward.
3 – Pressure Reversal
Gas moves to the outlet chamber when the pressure reverses. This causes the opposite diaphragm to flex.
The inlet check valve gets blocked, and the outlet check valve opens up, allowing fuel movement.
4 – Fuel Outlet
As fuel gets pushed out the outlet tube, more is constantly pulsing in from the other side.
Fuel movement happens incredibly quickly, with only a tiny amount passing through at a time.
Depending on your RPMs, the Mikuni will perform up to 6500 pulses per minute.
At just 4 gallons per hour, a lot for a snowmobile, your fuel pump only moves about .0013 fluid ounces per stroke.
When it leaves the pump, gas travels by hose into the carburetor.
Snowmobile Fuel Pump Diagram
Snowmobile fuel pumps can vary slightly. Primarily it’s a difference in shape, size, and how many outlet tubes they have (1 or 2).
However, the overall design is relatively standard because this part always pulls fuel in, regulates the flow, and pushes it out the other side for the spark plugs and engine to turn into power through combustion.
Here are all the parts you find in a typical snowmobile carburetor.
- Inlet Tube – This goes from the gas tank to the fuel pump and is activated by negative pressure that pulls the fuel in.
- Fuel Pump Body Segments – Generally, there are three pieces to the fuel pump body, and when placed together, they form most of the bulk. The top, middle and bottom plates come together to make internal chambers and a place to hold all the other parts together. Screws around the edges of the pump hold everything together under pressure, so there’s no leaking and pieces don’t slide out of place as your sled moves along.
- Gaskets – Without these clever rubber parts to press between the body segments and the diaphragms, there would be no way to properly seal up the chambers inside.
- Diaphragms – These are thin, often transparent sheets of mylar with slight flexibility to them. The diaphragm, combined with positive and negative pressure, flexes down to create space and pull in gas or presses it out of a chamber by bending upward.
- Check Valves – The inlet and outlet check valves are small, specially shaped pieces with an even smaller central hole running their length inside. Check valves fit inside specially formed spaces in the middle of the fuel pump and regulate gas flow from one chamber to the next. Additionally, they prevent backflow when the diaphragms flex, blocking the hole of one at a time.
- Carburetor Line – This line creates negative pressure inside the pump.
- Outlet Tube – The tube on the other side of your fuel pump pushes precisely regulated amounts of gasoline out of the pump and into the carburetor.
How To Test Snowmobile Fuel Pump
Testing a snowmobile fuel pump can help you determine what the problem is.
Moreover, it’s a pretty straightforward process that most people can handle at home with the right equipment.
You will need a vacuum gauge and the ability to remove bolts. This process is easier with a friend to crank the engine for you, but you can do it alone if necessary.
- Open up your engine. On older snowmobiles, you only need to lift up the cover, but for newer models, you may need to unbolt and remove several different parts.
- Remove only the fuel inlet tube. This is the one that goes to the gas tank.
- Place your vacuum gauge, so it connects to the fuel inlet where the tube was before.
- Crank your engine.
- Check the gauge to see if there was a vacuum.
- Next, remove the tubing that runs from your engine’s crankcase and ensure there is a pulse in the hose.
- Now take off the line from the pump to the carburetor.
- Use your gauge on the spot where you just removed the line to the carburetor.
- Crank the engine again and check the reading to see if it indicates pressure when cranked.
Diagnosis For Fuel Pump Tests
Whether it’s the pump or hoses, you can tell based on what the gauge said while the engine was cranked.
Anyone can replace a fuel pump by disconnecting the lines and swapping it for a new part.
However, for $5 to $20, you can easily buy a fuel pump repair kit and avoid wasting a mostly good component.
I always recommend refurbishing when you can.
Here is a basic rundown of what the tests above mean for your fuel pump.
- If you discover your pump has everything as expected, a vacuum on the fuel intake, pressure on the carburetor line, and a pulse in the crankcase hose, then it’s probably not the pump itself. You should check all the hoses for holes, bad seals, etc.
- Unfortunately, if you have no vacuum on the pump’s fuel intake end, your fuel pump is defective.
- The pump is also defective when you have a vacuum on the intake, a pulse in the crankcase, and no pressure to the carburetor line.
Snowmobile Fuel Pump Problems
Any part of a fuel pump can have a problem. A crack in the body or gasket that doesn’t seal will let air inside.
A broken diaphragm or check valve will prevent the proper flow of fuel throughout.
Finally, a busted line will mess with the pressure inside, leaking fuel or sucking in air where it shouldn’t.
How Do I Know If My Snowmobile Fuel Pump Is Bad
You can usually tell if your fuel pump is bad without looking inside. There are several noticeable symptoms to look for that may be caused by your pump not working or not working hard enough.
Please check your fuel pump immediately if you experience any problems on this list,
- Your check engine light comes on when a fuel pump is bad. This may indicate other problems, but it also comes on when there’s a lack of fuel pressure.
- Even if the check engine light doesn’t turn on, you can still have a bad fuel pump. If you turn the ignition and it reacts, but the snowmobile doesn’t start, it may be the pump.
- Losing power or moving more slowly when you push the throttle means fuel isn’t moving efficiently, which may be caused by a faulty or broken fuel pump.
- When you get a crank noise that lasts longer than usual before the snowmobile starts may indicate fuel pump problems.
- Misfiring and engine stalling can also tip you off that your fuel pump isn’t running smoothly.
Helpful Tips To Know About How A Snowmobile Fuel Pump Works
Snowmobile fuel pumps are surprisingly simple once you understand what they do and why. These parts are made of just a few components, making them easy to disassemble, diagnose and repair.
Here are more helpful tips to know about how a snowmobile pump works.
- Not all fuel pump issues are inside the pump itself. A cracked or broken line won’t pressurize or move fuel efficiently. Even the tiniest pinhole can wreck the hoses that attach to your fuel pump.
- Before fuel goes into the pump, it gets filtered. The fuel filter is attached to the inlet fuel line. Depending on your model and components, the filter should be inside the fuel tank or somewhere along that hose. This vital piece prevents debris from entering your fuel pump and tank. If the filter is missing, broken, or clogged, it can cause other parts down the line to get polluted gasoline which can gum up the works and prevent gas from reaching or flowing through the engine properly.
- Accidentally using the wrong gas can make your snowmobile run like the fuel pump is faulty. An E10 gas has less ethanol than, for example, E25. Unfortunately, while that E25 is higher octane, it also requires about 20% more fuel for the same operation. Your fuel pump, carburetor, and engine don’t ‘know’ the gas is wrong, and they can’t adapt, so you’d be running lean without realizing it. This can lead to most of the same symptoms of a faulty fuel pump, like stalling. I recommend double-checking your gas before you put it in the tank.
Final Thoughts
Snowmobile fuel pumps are pressurized. Negative pressure from the carburetor causes suction, allowing the pump to draw gas up from the engine and helps regulate where it flows.
Positive pressure from filling up reverses the direction the diaphragm moves inside to open up the next chamber, and the check valves let small amounts of fuel move through.
Once this is done, the gas flows through the outlet tube to the carburetor and on to power the engine.
Without a functional fuel pump, your gas would just sit in the tank, and your sled won’t move.