3 Reasons Your Snowblower Will Only Run on Choke

If you find your snowblower will only run on choke, you’ve come to the right place. The short answer to this problem is that your machine is encountering a lean air/fuel mix condition. Fix that, and it should be able to run without the choke.

Tools Needed (Commissions Earned)

Snowblowers, like other gasoline engine driven outdoor power equipment, rely on the correct ratio of air to fuel. This allows the engine to combust the mix appropriately in the combustion chamber.

If the mixture is too high, this is called a “rich” condition. It can lead to vapor lock and a stalled engine.

A mixture that is too low is called a “lean” condition. This will result in an engine that dies as well, especially when the choke is removed.

The air and fuel are mixed to obtain this ratio inside the carburetor. The choke is a butterfly valve that controls the amount of air entering the carburetor.

In normal operation, you turn the choke fully on to start a cold engine. This almost closes down the passage of air into the carburetor. It creates an intentionally rich condition to help start a cold engine.

Once the engine heats up, it no longer requires the rich starting condition, so you open the choke in order to allow the appropriate amount of air.

Unfortunately, if the machine dies when you turn off the choke, this means that it is getting too much air, and the mixture is too lean.

So what causes this lean condition?

Old Fuel

Gasoline diminishes in octane and flammability as it ages. It’s actually the fuel vapors that are igniting in the combustion chamber, so if the “explosiveness” of the fuel has decreased, it will need more fuel to compensate.

Only, the fuel is metered by the jets of the carburetor. Since that is a static variable, it cannot get more fuel. This results in too much air, and a lean condition.

Drain and replace the fuel if it is suspect. If that corrects the problem, that’s great! If not, move on to the next step.

Air Filter

Or possibly, the lack of one. The air filter is designed to clean the air coming into the carburetor to catch debris and dirt. The carburetor is designed with the air filter in mind. 

Since the air coming into the carburetor is normally restricted by the air filter, this is predetermined drag.

Hypothetically, if the air filter is missing altogether, this will result in too much air entering the carburetor once again. On the other hand, if the filter is completely plugged with oil and/or debris, this can result in a rich condition since the engine won’t be getting enough air.

Carburetor Jets

The third possibility is a dirty carburetor. Specifically, the jets of the carburetor. Depending on the type of carb, there can be several jets. These tiny orifices are where the fuel is drawn through. 

If they’re plugged, then the engine once again can’t get enough fuel and a lean condition is created. Since the engine is running on choke, it’s clear that the jets aren’t completely plugged. But, they still might be restricted.

You can try removing the float bowl and spraying some carburetor cleaner into it while on the machine, but I prefer to remove it altogether. This gives me an opportunity to disassemble the carburetor and soak it in my ultrasonic cleaner.

Doing so provides the best chance of success. Unfortunately, there are times where the restriction has developed with the passages of the carburetor casting itself. These can be exceptionally difficult to clear, even with an ultrasonic cleaner.

Rest assured, if your engine dies when you remove the choke, it is an air/fuel mix problem. I would be comfortable replacing the carburetor to rectify the problem if you can’t get it clean.

Recap

If your snowblower will only run on choke, you can confidently identify this as an air/fuel mix issue. From there, look into the components that determine the mixture. The fuel, air filter, and carburetor. All of these issues are easy to identify, repair or replace. 

Did I forget anything? Let me know in the comments below!

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