Snowblower Surging Idle

A constant surging engine is a real pain, but luckily it’s usually an easy fix. I’m a mechanic and surging is one of the most common types of complaint I hear. Not to worry, ten minutes from now you’ll know how to fix it too.

The most common cause of a surging snowblower at idle is a blocked carburetor idle jet. Removing, cleaning and refitting the idle jet commonly fixes the issue.

In this post you’ll learn how to diagnose why your snowblower is surging at idle and how you can fix it.

Mower gas cap

Vented Gas Cap

Blocked Idle Jet

Your snowblower engine is a pretty simple motor, the carburetor, although small and insignificant looking, is more complex than it may appear.

The carburetor is tasked with mixing air and gas together very precisely, and supplying it to the engine on demand.

If the air (oxygen) to gas relationship gets out of spec, the motor won’t run right or maybe won’t run at all. An engine runs best at a ratio of 14.7 parts air to one part gas. It’s known as the AFR (Air Fuel Ratio).

Surging commonly occurs when the engine lacks gas, in other words the carburetor isn’t doing its job correctly.

Carburetors commonly employ two fuel circuits, a main circuit that supplies gas when the snowblower is under load (moving snow) and what’s known as an idle circuit and it’s job as you’ve likely guessed is to supply enough gas to idle the engine smoothly.

Surging can occur when the engine is under load or when at idle, since yours is surging at idle we can be pretty sure the idle jet is likely partially blocked.

Cleaning the jet usually fixes the problem right up

Mower gas tank

Winged & Threaded caps

Idle Jet Cleaning

The carburetor works hard, it processes a lot of gas and air and over time dirt collects inside the bowl and the jets.

A thorough cleaning every few years is advised, however the carburetor needs to be removed and stripped to nail this procedure successfully.

Cleaning the idle jet is for most carburetors a lot less work. Many manufacturers allow for easy access and only a few tools like screwdrivers are required.

The process is simple and looks like this:

  • Locate the idle jet port (usually accessed from front of carburetor)
  • Remove the jet (screw or pressed fit)
  • Using fine wire clean the jet (I use wire brush strand and carb cleaner)
  • Clean the idle jet passage
  • Refit jet
  • Test engine
Vented mower gas caps

Vented gas caps

If the engine continues to surge at idle, and the idle jet is adjustable. Make it richer by opening the adjuster. If the engine continues to surge, consider removing the carburetor stripping including the welsh plugs and cleaning all ports.

As an alternative replacement carburetors aren’t expensive or difficult to fit. Just go ahead and replace the carb, especially if the snowblower is more than 10 years old or the carburetor is gummed up.

I advise all my customers to use a fuel stabilizer during storage. Gas goes stale and causes gumming of the carburetor, a common cause of surging.

The fuel stabilizer prevents gumming and keeps the gas fresh for up to 2 years. You can check out the stabilizer I use here on the “Snowblower maintenance tools page”.

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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.