When Should You Use A Choke On A Snowblower?

A choke lever is a strange concept for many. But for those of us old enough, (1970’s kids) the coke lever is a familiar ritual when starting the family car. I still remember starting my fathers car, using the choke does require a little finesse. But once you learn how it works, there's no mystery to it.

A snowblower choke is only used to start and warm the engine. To correctly use a snowblower choke, follow these 4 steps:

  1. Set choke control to “Full”
  2. Start engine
  3. Reduce choke to ¾ or ½ immediately
  4. After engine warms up, set choke to “Off”

In this post you’ll learn how to identify choke when and how to use it. You’ll also learn how it works, symptoms and the danger of excessive choke. In addition you’ll learn why some snow blowers will only run with choke applied.

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Vented Gas Cap

How To Identify Choke

The choke control lever on many machines is incorporated in the throttle control. Some manufacturers use the choke symbol to identify the choke and others may simply use the word “Choke” on the lever bezel.

It’s not uncommon for the choke lever to be located at the carburetor itself. When it is, the choke symbol may be embossed on the air filter cover to help identify choke “On” and “Off” positions.

The choke symbol represents a choke plate in the closed position, it takes a little imagination. See picture attached.

More modern and expensive snowblower engines may employ Auto choke and of course won’t have a choke lever or symbol since there’s no action needed to apply the choke.

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When And How To Use Snowblower Choke

To start a cold snowblower engine successfully, it will need choke. Many snow blowers will warm up after idling the engine for just five minutes or so (ambient temperature dependent).

It’s important to allow the engine to warm up before moving to full throttle. Engine oil when cold is thicker than when it’s warm. Allowing the oil to warm a little before going to work helps the oil do its job and coat all the components of the engine.

Most engine wear occurs because of a lack before and during the warm up period.

Vented mower gas caps

Vented gas caps

Starting a cold snowblower engine

Best to check oil is when the engine is cold. I advise my customers to check the engine oil every time they fill the gas tank, or at least once a week during the on season.

Follow these simple steps to start a cold engine:

  • Set throttle to full
  • Identify the choke lever and set to full
  • Start the engine
  • Move choke to ¾ or ½ on position
  • Move throttle back to ¾
  • Allow engine idle
  • As engine warms up, progressively reduce choke

You’ll know when the warm up cycle has finished, the engine will run smoothly without a choke.

Great job, now that’s how you warm up an engine using the choke.

Starting a hot snowblower engine

Starting a hot snowblower engine is usually identical with the exception of the warm up period. It should be noted that many won’t need any choke at all to start when hot.

Here’s the process for those snowblowers that need a shot of choke on hot start:

  • Set throttle to full
  • Apply ½ choke
  • Start the engine
  • Move choke to “Off” position immediately

How Snowblower Choke Works

The choke control is very basic on most snow blowers. Usually, it consists of a lever, cable and a choke plate within the carburetor. Pulling on the lever, tightens the cable which in turn closes the choke plate.

The choke plate is so called because when closed it restricts or chokes off the air supply.

Choking off the air supply to an engine we are trying to start admittingly sounds counter productive. But there’s no real mystery to it. As you know, cold air is denser than warm air.

Meaning a measure of air contains far more oxygen when cold than hot. Oxygen and gas are what a carburetor is designed to mix, and it must do so very precisely in order to run smoothly.

The optimum relationship or ratio is 14.7 parts air (oxygen) to one part gas. It’s known as the AFR (Air Fuel Ratio) and your snow blower’s carburetor is calibrated (hot) to mix the air and gas to this ratio.

Problem is, when the air and engine is cold the ratio is out of spec. The mix, if you like, contains too much oxygen. Another way to look at it, there’s not enough gas in the mix.

So there’s two ways to solve this imbalance, reduce the air supply or add more gas.

All snowblower are fitted with a choke and they come in one of three flavors:

  1. Choke plate
  2. Primer bulb
  3. Auto choke

Choke Plate: By far the most common type. Applying the choke plate type actually both restricts air (oxygen) supply and increases gas supply. It is the most effective choke type however it requires adjustment from time to time.

Primer Bulb: Indeed some snow blowers don’t employ a choke plate at all; they add a rubber priming bulb. Pressing the bulb adds extra gas to the carburetor for cold starts. It’s the simplest type system but tends to be a bit crude.

Auto Choke: A snowblower with auto choke employs the choke plate type, but also a mechanical thermo switch that senses engine heat and progressively removes choke proportional to warm up.

This is fitted to the more expensive type snow blowers and are pretty durable, however the thermo sensors do need to be replaced in time.

Symptoms Of Excessive Choke

Excessive choke means for the most part, forgetting to turn the choke off after the warm up period. This is a very common occurrence and has some lasting effects on the engine, we’ll talk a little about that in the next section.

While operator error is the most common cause of excessive choke, it’s not the only cause.

Other reasons the choke may remain On, include:

  • Choke plate binding – clean carburetor
  • Choke cable maladjustment – adjust cable
  • Choke lever/cable binding – free cable (WD40) or replace

The symptoms of excessive choke include the following:

  • Engines runs poorly
  • Engine sputters
  • Air filter wet
  • Black smoke from muffler
  • Excessive smell of gas
  • Engine flooding
  • Spark plug fouling

Dangers Of Excessive Choke Use

Running a snowblower with the choke set to the on position won’t do any damage in the short term, however consistently running the engine with the choke on will have some harmful results.

Running with the choke on or partially on will cause gas to dilute the engine oil. The oil is there as you know to protect the engine internals from friction. In addition, excessive gas inside the engine washes the layer of protective oil from the cylinder wall.

This usually results in either excessive engine wear or the engine seizes solid. In both cases it, likely more economic to replace the engine than to repair it.

Dangers Of Excessive Choke Use

A snowblower that only runs with the choke partially applied is a common complaint. It usually happens at the start of the new season and the root cause is usually a dirty carburetor.

Grit or debris in the fuel system or carburetor restricts gas flow and as you know that causes an AFR imbalance. Applying the choke helps because it restricts air flow and allows the engine to run smoothly.

But while the engine may run smoothly with the choke set to on, it is not running to capacity and you may find the engine loses power when you enter the snow.

The only solution is to clean the carburetor.

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Auto Technician and Writer at Lawnmowerfixed | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.