By: Author John Cunningham. Published: 2021/06/15 at 6:02 pm
A constantly 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 complaint types. Not to worry, ten minutes from now, you’ll know how to fix it.
A blocked carburetor idle jet is the most common cause of a surging snowblower at idle. 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.
Blocked Idle Jet
Your snowblower engine is a pretty simple motor; although small and insignificant looking, the carburetor 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, the main circuit that supplies gas when the snowblower is under load (moving snow) and what’s known as an idle circuit. As you’ve likely guessed, its job 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.
Idle Jet Cleaning
The carburetor works hard; it processes a lot of gas and air, and dirt collects inside the bowl and the jets over time. A thorough cleaning couple of years is advised; however, the carburetor must be removed and stripped to nail it successfully.
For most carburetors, cleaning the idle jet is 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:
Not all carburetors have an idle jet; if yours doesn’t, go ahead and clean the carburetor bowl feed jet (if fitted) and test. If surging continues, clean the emulsion tube also.
If the engine surges at idle, we can try adjusting the air-to-fuel mix. All carburetors have an AFR screw, but your adjusting screw may be decommissioned because of emissions laws.
Anyhow, check out the image below to help identify its location.
To adjust your AFR mix, turn the idle air screw (see image) (not the idle screw) counterclockwise until the engine stumbles, then turn it clockwise until it stumbles, and now back it out to the mid-way position between the two stumbles.
You are a pro!
If you can’t adjust your AFR, and the engine continues to surge, consider removing the carburetor stripping and cleaning, including the welch plugs, and cleaning all ports.
Replacement carburetors aren’t expensive or difficult to fit. Replace the carb if the snowblower is over ten 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 carburetor gumming, a common cause of surging.
Check out the gas stabilizer mixing ad adding video here.
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.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.