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How to Fix a Snow Blower That Runs Only When Priming

How to Fix a Snow Blower That Runs Only When Priming

When it’s time to clear the foot of snow that fell at night, the one thing you do not want is a snowblower that won’t work. One problem that sometimes occurs is a blower that only runs when you keep pressing the primer and stops running as soon as you reduce the choke. How can this be fixed?

Fixing a snowblower that needs constant priming starts with adjusting the carburetor so that the engine gets an adequate amount of gas. Other solutions include making sure the fuel filter is clean and that there is no fuel blockage to determine if excess air is entering the carburetor.

If your snowblower keeps stalling, you are not alone. This problem frequently happens, especially after the blower has been stored all year. Read on to find out what could be causing this and how to fix the problem.

How Primers Work

A primer bulb works on the vacuum principle. At its simplest, when you press down on the bulb, you create pressure inside the carburetor. When the bulb pops into its original shape, suction pressure lifts air up, creating a vacuum that allows gasoline to move down the fuel tube.

The primer isn’t an empty bulb, like a mini balloon. When the bulb is pressed down, air opens a one-way valve, often called a butterfly valve, that lets air into the fuel lines. Next, the air travels down the return pipe back to the fuel tank.  

So why doesn’t the air that went down the fuel line come back as the bulb returns to its original position? As the bulb does so, the butterfly valve that opened to push air toward the tank has now shut. If the carburetor is working correctly, then the various diaphragms, the metering lever and spring, and the other carburetor parts work together to create the proper air-to-fuel ratio.

Potential Problems and Their Fixes

The engine is sending a signal when it won’t run unless you are constantly priming—it needs more fuel. Any of several reasons could be causing this fuel starvation.  

Blocked Fuel Filter

If a fuel filter is dirty, then not enough fuel will flow through the filter, into the fuel pipe, and then through the carburetor. This will affect the fuel-to-air ratio, and the engine is now getting too much air and not enough fuel (source).

This is an easy fix. Check your filter. If it is dirty, then it is time to replace it with a new one. 

Fuel Tank Cap Breather

If the fuel filter is clean and working correctly, the fuel tank cap can be the culprit. As the engine continues to use fuel, the gas tank is emptying. This creates a vacuum in the fuel tank. A breather valve in the tank cap allows air to enter the fuel tank to prevent the vacuum.  

However, if the cap is blocked or damaged, it will not allow air in, thereby creating a vacuum in the fuel tank. This will again affect the fuel to air ratio and create the fuel starvation situation. If the breather is partially blocked, then pressing the primer offsets the limited gasoline.

If the cap is completely blocked, the engine will stop once too much vacuum has been created in the tank. In this situation, you will unscrew the cap to check on the fuel. Doing so, of course, allows more air in. Now the engine will work again until another vacuum is created in the fuel tank.

To see if this is the problem, you need to find a quiet place and slowly undo the fuel tank cap and listen. If you hear a hissing sound, then air is entering the tank to fill the vacuum.  

The solution is to either get a new breather for the cap or get a new cap.

Worn Fuel Pipe

The rubbery fuel pipe that sends gasoline from the tank to the carburetor gets cracks and wears out over time, drawing in air from the tiny cracks, which again causes too much air and not enough fuel. The fuel pump is now working harder, creating a vacuum.  

After you have checked your air filter, it’s a good idea to see if the fuel pipe is cracked.  

Fuel Blockage

There are many places where you could have a fuel blockage, most likely caused by dirt or crud build-up. If any of the fuel lines are entirely blocked, the engine will not start. However, a partial blockage would allow the engine to start, but it will sputter out if you do not press on the primer as it would not get enough gas.

The best solution for this problem is not to have it happen by using recommended gas, adding fuel stabilizers, and proper maintenance before storing it. In this case, prevention is better than the cure, which is cleaning the carburetor.

Loose Carburetor or Cracked Seals

If your machine has worked fine for several years and you have maintained it well, then the problem could be at the intake manifold, which is the point where the carburetor connects to the engine. If the carburetor has come loose from the manifold, the slight gap allows excess air to enter.  

Physically check the carburetor and see if it is loose and examine the area around the bolts. Make sure that the bolts that connect the carburetor to the manifold are tight. If they are loose, tighten them to get a snug fit. Do not overtighten them and strip the thread.

Visually inspect the gasket between the carburetor and intake manifold. If it looks brittle or has cracks, then it needs to be replaced.

Carburetor Screw Adjustments

The small adjustable screws on a carburetor control a small inlet that allows for more precise adjustments to get the right fuel to air ratio. If these screws are too far in, they will restrict the amount of fuel, again causing problems with the fuel-to-air ratio.

Adjusting the screws until you no longer need to prime continuously should solve this problem. Consult the owner’s manual for specific instructions on how to do that.

Metering Diaphragm Gasket

The gasket at the bottom of the carburetor needs to be sealed tightly. The small retaining screws should be tightened correctly. If these are loose, then the metering diaphragm and the metering lever won’t work the way they are supposed to.  

Make sure you tighten the screws at the bottom of the carburetor.

The fuel pump diaphragm can also get damaged or wear out. It’s a good idea to have it replaced when you get the engine serviced. Since you will not be able to see inside the carburetor to see if it’s damaged, don’t skimp on the replacements.

Storing the Snowblower at the End of the Season

To prevent the same problem from occurring next year, here are a few storage solutions to try out:

  • Empty the tank. As gas degrades, it causes gunk to build up. Instead of having to deal with a carburetor or fuel lines next winter, empty the tank. Just run the snowblower until it stops.
  • Seal the engine. To seal the engine chamber, use this simple hack: remove the carburetor, add a drop or two of engine oil into the chamber, and pull the starter cord three or four times. This lubricates the piston. Then put the plug back in and pull the cord again. When you feel some resistance in the cord, you have sealed the chamber, thus preventing moisture from entering the chamber. 
  • Clean. If snow where you live is treated with salt, you likely have salt on your snowblower. Take a few minutes to wipe it down.

Bottom Line

If your snowmobile won’t run unless you continuously prime the carburetor, the problem is almost always because the engine is starved of fuel. In some instances, there could be a blockage, such as when the filter is dirty. But many times, the problem is related to air leakage. In either case, you will need to troubleshoot through the various solutions, saving taking the carburetor apart as a last resort.