Lawn mower carburetor tuning. Lawn Mower Engine Surging – Check this easy fix first

Lawn Mower Engine Surging – Check this easy fix first!

Lawnmower engine surging is a right pain in the Jacksie; it’s an engine that runs erratically and revs up and down by itself uncontrollably. In some cases, it may only happen under certain conditions, for example, only after the mower gets hot or only when the fuel level gets low.

So what causes the lawnmower engines to surge? The most common reason for a surging lawn mower engine is a blockage in the fuel supply, but there are other possibilities:

Often you’ll find playing around with the throttle helps or applying some choke. You are not on your own; this is a regular complaint. In this guide, we will cover the diagnosis, likely causes, and solutions.

Try the easy fix first – replacing/cleaning gapping the spark plug before attempting carburetor work. If your mower engine is a Honda or Kohler, the fix is simple. Honda and Kohler’s surging is commonly caused by a blocked idle jet see “Gas starvation” towards the end of the page.

If you need more help, check out the “How to fix a surging mower video.”

If your surging mower is a Honda, check out the “Honda mower surging video.”

For many mowers, the fix is to replace the carburetor, and as carburetors are inexpensive, it just makes sense to swap it out and save a ton of messing around. You can check out the quality carburetors available and conveniently delivered to your door by Amazon.com.

Need more info on the fuel system, carburetor components, and how they work, you can check them out here.

Briggs Stratton Surging

Surging BS Classic 450, 500, or 550Some engine types are famous for surging; the Briggs Stratton 450, 500, and 550 series engines are fitted with a metal fuel tank and priming bulb-style carburetor. If you have one of these types of engines and it’s surging – You’re in the right place.

If you don’t have this type of carburetor, skip this section and jump to “Surging Test” below. These engines are fitted with a metal fuel tank and carburetor combination. The gasket sandwiched between the tank, and carburetor distorts over time, allowing a vacuum leak.

The vacuum leak causes the surging; replacing the gaskets and cleaning the carburetor/tank will leave it like new, I promise. In this tutorial, we’ll remove the tank/carburetor unit, clean it and replace the gaskets. Just some basic tools are needed, but get yourself a can of carburetor cleaner; it makes the job a lot easier.

In the workshop, I use WD40 carb cleaner, and you can check out all the tools and parts I use here on the “Small engine repair tools” page.

Tools You’ll Need

Here’s a short list of tools you’ll find useful to complete the task of fixing your surging mower. These tools aren’t essential, but they do make the whole job a ton easier; you’ll need:

Fuel treatment – Every small engine owner should use gas treatment. Most people don’t know gas goes off, and gas left in small engines can cause real problems, as you already know.

Using a gas stabilizer will keep the gas in your mower and your gas can fresh for up to two years.

Carburetor gasket – If you’re fixing the BS Classic engine, then you’ll need this gasket set.

Complete carburetor – As an alternative to replacing your BS Classic carburetor gasket, replace the complete carburetor instead; it includes the replacement gasket.

Manifold – This will only be needed if you have confirmed it has failed. Note there are a few different types of manifold pipe, so be sure to check before ordering.

You can check out all these tools on this page “Carburetor Surging Repair Tools.”

This carburetor style is fitted to a few engines and is prone to gasket failure. The job of replacing is simple and will solve the surge. The process is as follows:

Remove the spark plug wire – prevents the mower from starting.

Remove – Remove and clean the air filter and filter housing – Clean it using soapy water, and when dry, smear some engine oil over the surface of the foam. This helps trap dirt.

Remove tank bolts – They hold the fuel tank to the engine.

With fuel tank bolts removed – pull the tank unit straight out gently and remove the governor control link.

Remove the black rubber elbow crankcase breather pipe. Remove the manifold seal and keeper ring. Sometimes they will come loose and get stuck on the manifold pipe.

Remove – Remove carb screws from the carburetor and set aside.

Using a can of carburetor cleaner – clean all the ports on the surface of the fuel tank.

Empty the tank and rinse it out with fresh gas.

Pull the Siphon from the carburetor; they can be stubborn. Remove both gaskets and use carburetor cleaner to clean the siphon metal filter and all ports of the carburetor. Check the primer bulb for damage; mice like to eat them.

Spray – Spray the carburetor with carb cleaner.

Remove – Remove old gaskets and discard them.

Careful of this spring; it lives under the gaskets, and it can drop off and be tricky to find, as I know only too well.

The gasket is a two-part kit; the rubber-type gasket faces the tank. (carb fitted here for demo only)

The Siphon pushes back into the carb with a click. If you don’t hear the click, it’s not right – try again.

Refit the carburetor to the tank. Don’t over-tighten the screws, as this will distort the gasket. Fit manifold seal and keeper. Smear a small amount of oil on the seal; it helps it seat.

Clean the intake manifold. The grey tube in this shot is manifold. Inspect it for any signs of damage; they are prone to cracking. This will also cause a surge.

To fully inspect the pipe, you need to remove the pull assembly.

I would only do this if there was obvious damage to the manifold or if I had replaced the carburetor gasket and the engine was still surging.

This manifold is cracked and will cause a surge.

Before refitting the tank, fit the keeper ring and O-ring seal. Lube the seal before refitting the gas tank.

Offer the carb/tank unit up to the manifold and attach the governor link and spring. Now push the unit firmly onto the manifold. Fit both bolts.

Refit the air filter and spark plug wire. Use only fresh gas; make sure your gas can is clean. Gas older than three months is stale.

If, after fitting the gaskets, you still have a surge – Replace the Manifold.

Surging Test

As you know, gas starvation causes an inconsistent flow of fuel which in turn causes erratic running. And you also know a vacuum leak will cause erratic running, but it is a much less common cause; however, some carburetors are prone to vacuum leaks.

As engine manufacturers strive to make their engines more efficient, they have also made the carburetors more likely to clog; this has become a common issue.

To quickly diagnose which problem you have, a clogged carb or vacuum leak, follow this simple test.

You will need a helper to hold the bail lever or improvise with duct tape. CAUTION careful where you place your fingers and toes; the engine will be running, so the blade will be spinning.

Your mower will have a Manual choke, Auto choke, or a Primer bulb. Identify which type your mower has; the test is slightly different for each.

If you have a manual choke – apply half choke with the engine running.

If the engine now runs without surging – Gas starvation is the likely fault. If it runs just the same – A vacuum leak is a more likely fault.

If you have an Auto choke – Remove the air filter cover and filter – place a clean rag over the intake while the engine is running.

If the engine now runs without surging – Gas starvation is the likely fault.

If the engine runs just the same – A vacuum leak is the more likely fault.

If you have a primer bulb – you can still do the test – while the engine’s running (need a helper); give it some extra gas by pressing the bulb.

If the engine now runs without surging – Gas starvation is the likely fault.

If it runs just the same – A vacuum leak is a more likely fault.

Gas Starvation

If the test revealed gas starvation, it also showed that your problem is likely a dirty fuel jet in the carburetor, or the gas may be stale or contaminated by water.

Cleaning the main jet usually does the job.

Idle Jet Surging – Honda and Kohler use a relatively easy-to-access idle jet that clogs up and causes surging. The Kohler is easier to access than the Honda.

The Kohler is easier to access than the Honda.

Briggs has fitted a plastic carburetor to a range of engines which also clog up and cause surging.

All of these carburetors can be repaired by cleaning, which I’ve covered previously in videos (links below). Videos cover step-by-step removal, cleaning, refitting, and adjusting your carb.

Fixing this is not difficult. Sometimes you can get lucky by just draining and cleaning the gas bowl, which only takes a few minutes.

I have written a complete guide to Carburetor cleaning with pictures; it includes the gas bowl clean-out, which, as said, is worth trying first.

If cleaning doesn’t work out for you, go ahead and swap out the carburetor for a new one. Check out “New lawn mower carburetors page,” here, I’ve listed good quality replacement carburetors for all the most popular engines.

Carburetors aren’t expensive; messing around with them doesn’t make sense.

You might find this page helpful too – “Carburetor repair tools” I’ve listed some really useful tools that make the job easy. Some of these tools I’ll bet you already have some.

But do try cleaning the gas bowl before removing the carburetor.

Finding a Vacuum Leak

Air that enters the combustion chamber without passing through the carburetor is un-metered. This means the fuel-to-air ratio is unbalanced and, in turn, causes erratic engine performance.

When air sneaks in like this, it causes the engine to run lean (lacks gas). A lean engine runs hot, which isn’t good for an engine, especially an air-cooled one.

Vacuum leaks usually occur because of damaged gaskets. Gaskets are sealing materials fitted between the mating surfaces of engine components. Their function is to create an airtight seal.

They are commonly made from paper, felt, cork, Teflon, neoprene, metal, and rubber. The material type is dependent upon where the gasket is to be used.

Gaskets wear out and break down, and that causes surging.

Extreme Caution – You need to be careful, the engine will need to be running, and so the blade will be spinning when running this test.

A vacuum leak check is performed with the engine running and a can of carburetor cleaner; WD40 works, too, (is there anything WD can’t do?)

Spray the cleaner around all carburetor gaskets anywhere the carburetor meets the engine. The trick is to hear an instant change in engine note; that’s the sign of a vacuum leak.

This can be challenging; you must train your ear to notice the instant change in engine note (and not the surging).

Just do a small section at a time; this will allow you to pinpoint the failure area. Jumping the gun and replacing gaskets without finding the actual leak may work out for you or leave you with the same problem after the rebuild.

You’re right in thinking carburetor gaskets usually cause the problem, but other components, such as manifold pipes, can crack or become loose, causing surging.

Fixing A Vacuum Leak

If a leak is detected, replace all carburetor gaskets, and as you have the carburetor removed, go ahead and clean it. Replacement gaskets are available online; you will require the make and model numbers from the engine.

All manufacturers will have a model number printed on a sticker placed on the body or on the engine. Have a poke around; you’ll find it. Most engine manufacturers will stamp the model numbers in an accessible area. Briggs Stratton stamp their numbers on the metal engine cover.

A new carburetor comes with new inlet gaskets; I like to fit original parts where I can; they fit and are guaranteed.

If, after replacing the carburetor gaskets, the engine still surges, you’ll need to go a little further and replace the manifold intake and gasket.

It’s not a big job, and they don’t give a lot of trouble, but they do crack as they get older. I wrote a step-by-step guide showing you everything you need to know – “Briggs Manifold Replacing.”

Related Question

Honda lawn mower surging fix? To fix a surging Honda lawn mower engine, clean the carburetor, gas tank, and fuel filter. Use fresh regular gas or e10. What causes a lawnmower to run slowly? The most likely cause is a throttle linkage bent out of shape by bumping into the shrubbery or a throttle spring has detached itself.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

And the best part. it’s free!

Lawn Mower Parts

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Feel confident in tuning up your lawn mower or garden equipment this season with our Home Maintenance Kits. Easily find the right product so you can DIY and save!

Looking for your Serial Number?

Finding your lawn mower’s model number and serial number is as easy as locating the identification tag on your machine. As seen in the example, the model number will be displayed below the MODEL heading (Example: Z235), and the serial number will be underlined on the top-right corner of the tag (Example: 130002).

If you’re looking for the engine number, that can be found directly on the engine itself.

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Get the latest on how to care for and enjoy your yard and garden. The articles and videos are informative and the ideas are amazing.

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Genuine John Deere Belts Blades are your best choice for your newer machines.

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The John Deere Easy Change™ 30-Second Oil Change System

Never drain engine oil again.

We’ve changed the oil change. Revolutionized it really. See how fast and easy changing your oil can now be on 100 Series Riding Lawn Tractors with the John Deere Easy Change™ 30-Second Oil Change System. Only from John Deere. Included on the E120, E130, E150, E160, E170, and E180 models.

Step One. Take it off.

Lift the hood. Make sure the engine is cool, then, twist to remove. It’s that simple.

Step Two. Twist and lock.

Grab the new Easy Change™ Canister, twist and lock into place. Make sure the arrow on your Filter System aligns with the arrow on your engine.

Step three. Done.

Close the hood and mow. John Deere recommends the Easy Change™ 30-second Oil Change System every 50 hours or at the end of your mowing season. Don’t drain engine oil ever again.

Draining engine oil is so 2017.

The engine modifications and new technologies are in. The re-envisioned oil filter with a media designed to resist breaking down in oil over time is here. The thousands of hours of testing are done. The end result is an all-in-one, oil and oil filter system like no other. The first of its kind. And thanks to the new John Deere Easy Change™ 30-Second Oil Change System (“System”), you’ll never have to drain the oil from 100 Series Riding Lawn Tractors again.

Here’s why: The new System captures contaminants and recharges your engine with nearly a quart (0.8qt) (0.76 l) of new oil. In fact, this System increases the amount of oil in the engine by nearly 40%. 2 Your engine likes that.

What do you mean, I will never have to drain oil from my engine again? How is that possible? The answer is simple. We have developed a better filtration system and filter design for our 100 Series Riding Lawn Tractors 1. This fully synthetic filter media has greater surface area which increases its capacity to hold harmful contaminants. What’s more, the filter media is designed to resist breaking down in oil over time. Which means you’ll get a cooler running engine. And a cooler running engine and better filtering helps increase engine oil life. John Deere’s recommended oil service for 100 Series Riding Lawn Tractors 1. is to change the System every 50 hours or once a season, whichever comes first. Remember, the System replaces a portion of your engine oil. And that’s plenty.

The System uses John Deere Turf-Gard™ Oil. Using John Deere Turf-Gard™ Oil ensures you are using the exact oil specified by John Deere engineers.

Testing. Testing. Testing. Thanks to thousands of hours of rigorous and extensive testing, you can feel confident your engine will run for years to come.

1 The John Deere Easy Change™ 30-Second Oil Change System is available on E120, E130, E150, E160, E170 and E180 Lawn Tractors today.

2 Compared to similar V-Twin engine models that do not have the John Deere Easy Change™ 30-Second Oil Change System. That includes equivalent Deere 2017 models and 2018 models without the System.

Frequently Asked Questions:

What is new with John Deere Riding Lawn Equipment?

We are excited about the exclusive John Deere Easy Change™ 30 second oil change system. Exclusive to John Deere and only available on certain models of the new 100 Series Lawn Tractors. These tractors are designed for ease of use for both operation and maintenance. The John Deere Easy Change™ System (“Easy Change”) allows the user to easily complete the recommended engine oil and filter maintenance in 30 seconds.

What is this new oil change system?

We changed the oil change. The all-in-one oil and oil filter system gives the owner the ability to change a portion of the oil and the filter in less than 30 seconds.

What happens to the rest of the oil in the engine when the Easy Change system is replaced?

The Easy Change system replaces.8 quart of oil. The remaining oil in the engine is refreshed by the charge of new oil included in the replacement Easy Change system. Combined with 40% more engine oil capacity, improved filtration and cooler running temperatures which help extend oil life, it is no longer necessary to remove and dispose of all the oil in your engine during service.

What makes the Easy Change system unique from other filters?

It is not just a filter. It is a newly developed technology system that allows a new “filter” to come already charged with oil and allows you to remove an existing filter and the contaminants inside without tools and without making a mess. Beyond the filter, technology within the canister and on your engine makes this possible.

Models with the Easy Change oil system use a fully synthetic filter that has more capacity to trap and hold contaminants. The larger surface area of the Easy Change canister acts like a radiator helping the oil to stay cool.

Does the Easy Change system somehow decrease the life of the engine?

The John Deere 100 Series lawn tractor models, with and without Easy Change, are specified for the same lifetime and are rigorously tested to the same standards to ensure the life of the tractor meets expectations.

Can I add the Easy change system to an existing tractor?

Because this system also requires unique features within the engine, the Easy Change system cannot be added to an engine that was not equipped with it at the factory.

Can I change all the oil if I choose to?

You could if you wanted to. There is an oil drain plug. It is not required for maintenance.

How often do I need to change the Easy Change canister?

Every 50 hours or once a year. The 100 Series Lawn Tractors with and without the Easy Change system have the same maintenance schedule.

What type of oil is recommended?

We recommend only John Deere Turf-Gard™ 10W30 Oil. The Easy Change canister comes pre-filled with John Deere Turf-Gard™ 10W30 oil.

How do I recycle the old oil?

Many local government recycling programs, authorized retailers, auto repair stations, and auto parts stores will puncture and recycle used oil filters and oil.

Do I ever need to add oil?

Yes. Consistent with our service recommendations for this product, you should check oil level daily and add oil if required.

What Should I do when my lawn and garden engine runs rough or has poor idle?

When your gas-powered lawnmower, trimmer or chain saw is running rough or doesn’t idle correctly, the annoying sound is just the start of your problems. When your equipment’s engine isn’t running smooth, performance suffers, leaving the job undone.

Causes:

If the engine starts, but does not run smoothly, it means that the spark plug and ignition system are in order and you need to look elsewhere for the source of the problem. The usual culprit is air intake or fuel system related.

Symptoms

Dirty or Clogged Air Filter

The job of the air filter is to remove dirt and debris from the air before it enters your engine. If the filter is doing its job, it may become clogged and not allow a sufficient amount of air into the engine for it to run smoothly, If the filter is dirty, it should be replaced.

Old Gas

When did you last fill up the gas tank? Old gasoline can affect the performance of the engine. Gas can go stale in as little as 30 days. If the fuel is old, it should be dumped into a container for proper disposal and fresh fuel should be added. Other options include adding a fuel stabilizer to your tank or using canned fuel that contains no ethanol.

Obstructed Gas Tank Vent

After adding new fuel, check the gas cap. In many small engines, the gas cap also has a vent that serves as the fuel tank ventilation. In order to work properly and supply a sufficient amount of fuel to the carburetor, the vent must be open and free of any debris.

Dirty or clogged fuel filter

A fuel filter that is dirty or clogged with debris can restrict the amount of fuel getting to the carburetor.

Solutions

Change air filter if it’s clogged or dirty.

Unclog or replace gas cap if air vent is blocked.

Replace dirty or clogged fuel filter.

Replace old gas with fresh gas (properly dispose of old gas).

If none of these tips get you up and running smoothly, then it’s time to call on a professional mechanic who specializes in small engines.

The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

Will It Run and Drive? Lawn Mower Carburetor on a Ford 302 V8 Engine

Luke Finley, ThunderHead289 on YouTube, is clearly fascinated with the science behind things and arguably could be described as an automotive technical geek. He of course likes fast and loud but is often more interested in what gets you there.

In this video, Luke steps way off the beaten path and attempts to adapt a float bowl-style lawn mower carburetor to the 302 V8 in his 1974 Ford Maverick with a four-speed gearbox. With gas what they are, his interested mind wants to know if this is practical, or even possible.

To make this work, Luke designed a lawnmower to 4 barrel square bore adapter designed with Fusion 360 and 3D printed over the course of 34 hours with PETG filament, a fuel-friendly plastic. He’s also 3D printed an air filter housing that works around Ford’s front-mounted distributor.

Will it RUN? Lawn Mower Carb VS Ford 302

He clearly states that “this should not work, on paper”, will his determination to make it work pay off…

Will it DRIVE? Lawn Mower Carb VS Ford 302

So, it idles, runs, and revs well and Luke now tries to drive his 302-powered Maverick fed by the lawnmower carburetor in place of the typical 390 4 barrel Holley.

He explains some of the theories behind why this may or may not work when trying to drive this configuration on the road.

“I wouldn’t have believed it if I didn’t do it myself…”

Luke Finley, ThunderHead289

Many viewers have commented that they believe this setup will be far too lean to run and drive practically, while Luke believes it will actually be rich, and clearly demonstrates why.

He also describes adjustments made to the ignition timing specifically for a rich scenario. This is very interesting stuff…

MPG Testing in a Lawnmower Fed Ford 302 V8 Engine

So, what kind of fuel mileage is this setup going to achieve? Luke points out that he did this initially for the absurdity, not necessarily the practicality of it, but ironically, it’s turned out to be pretty darn practical! In this video, Kuke hits the road in his lawnmower carb-fed ’74 Maverick to see just what type of fuel economy can be achieved…

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