Here’s What To Do If Your Lawn Mower Won’t Start. Lawn mower throttle spring

How To Troubleshoot a Lawn Mower That Won’t Throttle Up

Have you ever experienced a situation where you noticed that the throttle seemed to be stuck in one particular position, and you could not throttle up or down your lawn mower engine speed? If yes, you must have wondered whether it is possible to troubleshoot such a failure and if possible, how to troubleshoot a lawn mower throttle issue?

First, remove the top Shroud cover, Primer line and Fuel line. Then, remove the Air filter, Carburetor and Throttle control parts. Next, install the new plastic part, reinstall the carburetor and other rest of the parts.

Read the following article and learn to troubleshoot a lawn mower that won’t throttle up.

What Causes the Problem?

Throttle failure mostly occurs due to problems with the carburetor, faulty air filter, or throttle control parts such as the internal plastic element, rod, or cable.

The lawn mower will fail to throttle up and down properly if the throttle is stuck in between or the engine is not receiving the correct fuel mixture to start up.

In most cases, this trouble can be easily solved by cleaning, lubrication, and performing minor adjustments to the throttle cable.

But make sure you have found the actual issue which causes your lawn mower to encounter such trouble.

Steps to troubleshoot a lawn mower won’t throttle up:

Imagine you are middle of mowing your lawn or work field, and suddenly, you noticed that the mower just went on running half throttle, then visibly surges when you tried to run it on full throttle.

Or, you could not move your mower’s throttle up or down.

All you need is a quick way to troubleshoot and break into your mower throttle system to fix it immediately.

Things required to troubleshoot the lawn mower won’t throttle up:

Look at the checklist of the required tools and materials:

Tools Materials
larger Phillips screwdriver Plastic part replacement kit
Flat Screwdriver
Liquid Wrench
Safety Goggles Gloves

Step 1- Removing the Top Shroud Cover:

First, remove the three Torx screws on top of the Shroud cover.

Now that both screws are off at the back, you just have one left in the front end. So, remove the screw, and the cover will come off.

Tips: while removing the top shroud cover, you have to pry up a bit and be careful because the fuel line and the primer are still hooked up to the carburetor.

Step 2- Remove the Primer line and Fuel line:

Next, you need to disconnect the primer line, which is the smaller line out of the tube.

Usually, you can just pull it by hand, and it will come off like this.

Now, lift the cover, and you can see the fuel line on the other side.

So, loosen the fuel clamp and remove the show line from the gas tank.

Tips: You should empty your fuel tank before doing this removal task to prevent any leaking issue.

To prevent fuel from leaking out of the connector, keep the fuel tank tilted as shown in the image.

And leave the Cal to hang on the side as shown in the picture. Next, you might see a bit of fuel leak out of the fuel line.

The left-out fuel in the carburetor will come off like that.

Just get a rag to soak that up or leave one underneath while working.

Step 3- Remove the Air Filter and Carburetor:

First, take off the clips with a flat screwdriver to remove the air filter cover.

Now pull it open, and it is going to swivel out.

Now grab a larger Phillips screwdriver to number three and reach down inside to remove those two screws, that hold the carburetor in place.

As soon you remove the screws, the carburetor will also come off.

Step 4- Throttle control removal:

Now, you will see a metal plate and a gasket as shown in the picture.

Here’s the throttle cable end, and you can see a broken plastic part over there.

Thus, if you try to grab the throttle cable, you will notice its grabbing on nothing, and it cannot adjust the engine speed.

This is the small plastic part that’s missing.

To remove the part, you need to pop out the metal rod, and you need a good flat screwdriver for this task.

Just go under here and pry. Then do the same thing on the other side too.

You can either take the rod all out or take one side out and swing it like this.

Before completely removing the plastic part, take a good look at the little spring over here and make sure when you re-insert the part, you put the spring exactly in the same position.

Next, pull up and swing the plastic part around to remove it.

Step 5- Reinstall the Parts:

Remove the throttle cable by squeezing the tabs and pulling out there.

Now, this is the new part that I’m going to insert.

To reinstall this part, just follow the same procedure that you used earlier to remove it but in a reverse motion.

Next, grab the metal rod and bring it back over the plastic part into the hole.

The rod will clip into the grooves here on the plastic part. So just push down on the rod, and it’s going to go right.

Then, make sure the lever is all the way down.

Now, grab the throttle cable and stick it in the little hole.

Then, bring it back and push in the cable until these tabs click into the metal part.

Next, grab the carburetor screws and put them in over here.

Then grab the metal plate on the gasket and put it into the screws.

Hold the screws at the rare with your fingers and push them to the plate as well as the gasket.

Step 6- Reinstall the carburetor and test the newly inserted parts:

The carburetor and metal plate should be lined up and screwed in.

Hold the metal plate and screws on the carburetor with both your hands.

To insert this plastic flag underneath the Cawl, just tilt the carburetor, and you will see a hole under there.

So, bring it up like this and line up the screws to the hole over there.

Then, have your screwdriver ready to reach down inside and tighten up the screws.

Now, test whether the throttle cable and new inserted parts are working or not by moving the throttle lever back and forth like this. Then, log down over here to make sure that it is moving.

Before adding the rest of the parts, spray some liquid wrench on the plastic part to lubricate it.

After that, reinstall all the rest of the parts by following the same removal techniques but in reverse.

Performing such troubleshooting tasks can be hazardous. Thus, always be sure that you ‘ve enough expertise and read your mower’s instructions manual before operating, or troubleshooting it.

Frequently Asked Questions

What causes a lawn mower throttle to stuck in one position?

Due to the lawn mower engine receiving an incorrect fuel mixture to start.

What are the symptoms of a Bad or failing lawn mower throttle cable?

The most common symptoms determining bad throttle cable are wrong cable adjustment, slow or no acceleration response, dirty or frayed cable connections, and defective cruise control.

What causes small engine to die after filling it with gas?

The most common causes of such problems are over-priming, sealed/snug choke, stuck valve, or gummed carburetor.

What causes my lawn mower to not run-in full throttle?

Due to clogged air filter, contaminated gas, excess or too little engine oil, blocked fuel filter, dirty or defective spark plug, plugged carburetor, dull blade, or clogged cutting deck.

What controls the push mower’s throttle?

On most push mowers the throttle handle controls the throttle cable or engine speed.

Final Verdict

Initially, the entire process might seem a little complicated, but if you follow the given instructions in today’s article, you can fix your lawn mower’s throttle problem easily.

Remember, you can only get the best result if you thoroughly follow all the instructions to troubleshoot a lawn mower won’t throttle up.

Learn the reasons why a lawn mower won’t start after winter or during peak season, and how to fix those problems.

Family Handyman


Most of the time when a lawn mower won’t start the cause is a problem with the gas or the lawn mower carburetor.

What to Do if Your Lawn Mower Won’t Start

Whatever kind of lawn mower you’ve got, the last thing you want once winter finally lifts and spring has sprung is a lawn mower that won’t start.

If you’ve taken the proper steps to winterize your lawn mower, you’re far less likely to be dealing with such issues. It’s also why you should tune up your lawn mower at the start of every season. However, it’s not out of the ordinary to find your gas-powered lawn mower not starting from time to time, so it’s important to know why your lawn mower isn’t starting and how to fix it.

Project step-by-step (6)

Check the Gas Tank

Let’s start with the obvious. Before you have a heart attack pulling on the rip cord, you’ll want to check the fuel. Like any gasoline-powered engine, lawn mowers run out from time to time. Maybe you forgot it was running on fumes when you finished mowing last time. It sounds simple, but we’ve all overlooked the gas tank from time to time.

Even if there is gas in the mower, if the fuel’s been in there more than a month, that could be the problem. Gas sitting around too long in the tank can get contaminated with dirt and extra moisture.

So if your gasoline has been in the mower for more than month, drain the gas properly, dispose of it correctly, and fill up the mower with new gas. It may take quite a few pulls to suck the new gas into the lawn mower carburetor, so be prepared to clean and dry the plug a few more times.

Add fuel stabilizer when you fill up the tank to help protect the gasoline in there from dirt and moisture.

Family Handyman

Check the Spark Plug

Start by making sure the lawn mower spark plug cable is connected to the plug itself. It’s quite possible that it got pulled off there over the winter while the mower was being stored in the garage.

If that’s not the issue, the next step is to remove the spark plug to see if it’s wet. There’s no way the engine will start if it is. So clean the plug with carburetor cleaner and let it dry. Cleaning it with compressed air isn’t enough; you need a solvent to remove oil residue. If it’s really grimy and dirty, it might be best to change the spark plug.

Fertnig/Getty Images

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 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

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.

Lawn Mower REPAIR Auto Choke Briggs and Stratton Sears Craftsman fix engine won’t start spring

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.

How to Fix Lawn mower Engine Surging on Briggs & Stratton Lawnmower Engine!

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.

here, your, lawn, mower

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.

here, your, lawn, mower

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.

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. 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. It’s all covered in the video library. It shows you step by step how to remove, clean, refit, and adjust your carb. It’s a detailed, engine-specific guide, easy to follow, and only regular tools are needed.

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 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 so inexpensive; 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?)

here, your, lawn, mower

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.

Lawn mower throttle spring

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