My Lawn Mower is Not Getting Gas to Spark Plug [5 Fixes that Work]
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It is frustrating when your lawn mower won’t start. I’ve seen this problem even with new gas-powered mowers. After extensive diagnosis and experience, I’ve found the most common cause is that the lawn mower is not getting gas to the spark plug. But that’s not all.
When your lawn mower won’t start, chances are it is not getting gas to the spark plug. Common causes include a dirty air filter, spark plug, and carburetor. To fix these issues, replace the fuel filter, clean the carburetor and spark plug, and replace the fuel if it is old as illustrated below.
What causes my lawn mower not to pump gas to spark plugs?
Gas-powered lawn mowers need gas to be pumped into the carburetor in order to start. Should anything obstruct the flow of gasoline, the engine won’t start. And even if it does, it’s likely to fail after a couple of minutes.
Here’s what causes mowers to not efficiently pump gas to the spark plug and ignite:
A dirty air filter
The air filter on a carburetor cleans the incoming air of dust and other debris that could cause damage to engine parts. Over time, the air filter could get clogged up, thus affecting the flow of oxygen to the engine.
When the engine does not get enough oxygen that helps with fuel combustion when the spark plug ignites your lawn mower won’t start.
Manual choke left turned on
The choke is a shaft-mounted valve within the air intake chamber of the carburetor. Its function is to block the airflow for improved suction and consequently facilitate a more efficient engine start-up.
While some chokes are automatic, some mower motors have manual chokes that the user has to turn on and off by themselves.
If you leave a manual choke on several minutes after starting the mower, the carburetor will likely flood up, leading to starting failures the next time you try to start up your lawn mower.
Clogged filters in the fuel pump
powerful mowers, such as ride-along lawn mowers, make use of fuel pumps to pump gas into the engine – instead of the gravity-feeding system that’s common in most push-along mowers.
Stuck open valves
If the intake and exhaust valves don’t seal fully due to sticking, build-up of debris or normal wear and tear, compression is hampered, consequently creating ignition problems.
If the intake valve becomes stuck, this affects the efficiency of the flow of the air/fuel mixture to the cylinder, resulting in a lawn mower that won’t start.
Signs your lawn mower is not getting gas
There are several issues that could be causing your lawn mower not to run, including electric faults within the spark plugs as well as the causes I’ve listed above.
For instance- if your spark plug is wet, you definitely can’t get your motor to start. However- more often than not- the issue is usually caused by the cutting off of efficient fuel supply to the spark plugs.
Here are a few signs your lawn mower is not getting gas to the spark plug and won’t start due to the inability to pump gas to the engine:
Lawn mower won’t start completely
If you totally can’t get your mower to start, there could be issues with the efficiency of fuel flow to the engine.
- This is usually caused by debris collecting and blocking crucial components of the fuel intake system such as the throttle, primer button, carburetor bowl, and the fuel filter.
- A malfunctioned fuel pump.
Such clogging hampers the efficient flow of gas to the spark plugs.
Riding lawn mower starts then stops running
If your fuel tank is full, but your mower still comes to a stop after just a few seconds, it’s highly likely that the hole atop the tank’s cap has been blocked by dust and debris.
This cuts off the back pressure needed to push fuel out of the tank and into the carburetor – by cutting off air supply into the tank.
No gasoline odor
If you can’t get your mower to start and at the same time can’t sense any gas smell coming from the motor, your lawnmower has definitely run out of fuel.
Most mower brands typically include a dipstick attached to the screw cap. A dipstick is used to check the fuel level within the gas tank. It will typically have low and high-level markers.
- Dip the dipstick into the gas tank to check the gasoline level.
- If the fuel mark is below the low-level mark, it means you’re running out of gasoline and that’s why your mower won’t start.
In this case, refill the gas tank then try starting the mower again to see if the problem will have been fixed.
See also my guide on the type of gas to use with your lawn mower
How to Fix a Lawn Mower that’s Not Getting Gas
Some of these problems can occur when in the middle of mowing. A dirty spark plug, for instance, may cause your lawn mower not to have enough power for mowing. Fuel pump and filter problems too can make it not to start.
Here are simple DIY fixes you can use to correct the problem and start the lawn mower again.
Use fresh or new fuel
I found that for Craftsman mowers, old fuel tends to clog up the carburetors and cause difficulty in the flow of gasoline. As such, you should always ensure that the gasoline in your tank is as fresh as necessary.
- A good way of keeping stored oil fresher for longer is to use a gas stabilization product.
- Use a high-quality fuel stabilizer for small engines such as the Star Tron Enzyme Fuel Treatment.
This solution will prevent fuel degradation by reducing oxidation. Your fuel will stay clean and fresh for longer.
Replace the fuel filter
If you own a Husqvarna mower and it won’t start, the most likely cause would be a clogged fuel filter. This usually happens if you’ve left fuel in your mower for long.
The best fix is to drain off the old fuel from the gas tank and replacing the filter.
Clean the carburetor
For MTD mowers, the most common cause of fuel not getting to the spark plug is a clogged-up carburetor due to the buildup of debris.
To fix the problem, clean up the carburetor by taking out the fuel bowl and spraying the carburetor with some carburetor cleaner.
A clean carburetor will get your MTD lawn mower motor running again.
Here’s a video on how to clean the carburetor on your lawn mower:
Mower Won’t Start No Spark (This Is Why)
Pulling and pulling and nothing, a mower without spark, is useless. In this post, we’ll cover all the most common ignition system failures.
Mower won’t start any spark? Common reasons a lawnmower has no spark include:
None of these tests are difficult, and twenty minutes from now, you’ll know why your mower has no spark.This post will have you covered, but if you need video help diagnosing no spark or help to fit a new coil, check out “Mower won’t start video.”
Checking Lawnmower Spark
Since you’ve checked the spark already, I’m guessing you know the procedure. However, it’s worth pointing out, getting this test wrong can lead to misdiagnosing and replacing the ignition coil or other parts unnecessarily.
Spark testing is, as you know, a simple test, you won’t need any special tools here, but a spark testing tool does make the job easier and totally foolproof.
If you need video help, check out the mower “Mower spark test video,” where I cover the whole process.
Tools needed
For these tests, you’ll need a plug spanner, insulated pliers, screwdrivers, and a spark plug is useful. You’ll also need a helper, as we’re not using a spark testing tool. It can be difficult to crank over the engine and, at the same time, check for spark. With all the tools gathered and a helper on hand, we’ll get right to it.
Spark Testing
As we’ll have a helper cranking over the engine, that means the blade will be spinning, and even though the engine’s not running, it can still remove body parts, so, you know!
You must use insulated pliers (plastic/rubber-handled pliers) to hold the plug as the voltages produced are enough to give you a jolt, which isn’t pleasant.
Tools – Plug spanner, insulated pliers, and a spark plug will be needed.
Step 1 – Remove the spark plug wire by twisting and pulling, then using the plug tool, remove the spark plug.
Step 2 – Reattach the spark plug wire to the plug. Using your insulated pliers, hold the plug threads firmly against the metal of the engine. This is known as grounding. If the plug doesn’t make good contact with the metal of the engine, you won’t get a spark.
Step 3 – While you watch for spark, have the helper hold the bail lever as normal and yank on the pull cord.
If you have no spark, swap out the plug and test again.
If you still have no spark, it is most likely a failed coil, but best to check the on/off switch assembly first.
Common Spark Plug Faults
A healthy spark plug is essential for reliability, power, and smooth running. Plugs have a tough job. They carry high voltages and live at the heart of the engine where it’s hottest.
Making matters worse for the plug is its location – right out front of the engine. So getting shoved into fences and trees is all part of a spark plug’s life, and you thought you had it hard!These are the most common spark plug faults:
Wrong Plug Type
Plugs areas you know are graded; each engine will have a particular plug code. So even though a plug fits, it doesn’t mean it’s correct. Plugs are graded by heat. The plug should get hot enough to burn off contaminants but not so hot that it pre-ignites. Wrong plug types can cause all types of problems, from hard starting, rough running, hot start failures, etc.
Plug type – Check your plug type with your mower engine maker.
An incorrect plug type will lead to intermittent problems.
Dirty Plug
Self-explanatory, it’s a plug that’s contaminated by too much gas (flooding), carbon, or oil. All of these will prevent the plug from doing its job. Flooding may be caused for a few reasons – blocked air filter, faulty choke, overuse of choke, tipping mower over on its carburetor side, and carburetor fault. Check out the video “How to fix a flooded engine.”
Carbon build-up in the engine is a normal condition. Fuel type, oil type, maintenance, and plug type all affect how quickly it builds.
Oil on the plug is also common. It’s caused by too much oil, blocked crankcase breather, head gasket fault, engine wear, and wrong plug type. Check out the video “How to clean a plug.”
Bad Plug Gap
A spark plug function is obviously to create a spark, and it can only do this if the electrode gap is correct. The coil has been designed to create a sufficient spark to jump a pre-determined spark plug gap.
A plug gap tool is used to set the spark plugs gap. The electrode is manipulated to the correct size by simply bending it with pliers. Check out the video “How to gap a plug.”
Plug gap – The gap is important. Too small or too big can lead to no starts or poor running.
Cracked Plug Insulator
Self-explanatory too. The insulator is the white ceramic material of the plug’s body, and as said earlier, plugs are at risk of being damaged by bumping into obstacles. If the insulator breaks or cracks, the plug stops working.
Common Spark Plug Wire Faults
A spark plug wire has a few particular problems that affect them, depending on a few variables, like how and where they’re stored.
The common faults I see again and again include:
Loose Terminal
Caused by our old friends, the trees, shrubs, and fences. The plug wire terminal that clips to the spark plug becomes loose, and that can cause no starts, poor running, and intermittent starting/running.The fix here is simple, squeeze the terminal body using pliers to tighten it.
A loose terminal will cause the engine to misfire or not start at all. The quick fix here is to squeeze the terminal until it fits snugly on the plug.
Faulty Terminal
Because this cap was loose, it created arching, which burnt the metal of the terminal cap.
Faulty terminal connector – It’s different but related to a loose connector. A loose connector will often turn into a faulty one as the spark starts to jump inside the terminal, burning it or setting up conditions for corrosion to take hold.
The outcome is the same, no spark or poor running. A replacement terminal can be purchased and fitted to solve this issue.
Damaged Plug Wire
Plug wire rubbing off the engine cover can cause the insulation to wear and the coil to ground. But more often than not, a damaged plug wire means rodents. Mice love wiring insulation, and unfortunately, our furry friends have cost us a coil.
Sure, you can wrap them with insulation tape, but it’s only a quick fix. The long-term repair is to replace.
Damaged wire – Mice love to chew on the wiring insulation.
Common Stop/StartAssembly Faults
Most mower owners are familiar with the bail lever at the handlebars, which must be held to start the mower. Most mowers will use this type of stop/start system; other manufacturers may incorporate the stop/start function with the throttle lever. But apart from this difference, all other components will be very similar.
The main components of the stop/start assembly include:
Bail / Throttle Lever
Common faults here include disconnected, out of adjustment, or broken levers.
Cable
The cables break and stretch, so it’s not uncommon for the bail lever to work, but because the cable has stretched, it doesn’t move the brake assembly to the start position.
Flywheel Brake Assembly
Common faults here include cable out of adjustment, meaning the bail lever doesn’t pull the brake to the off position.
Stop/Start Switch
This is the on/off switch. It’s fitted at the flywheel brake assembly. When the bail lever pulls the assembly, it pushes on the switch removing the ground connection to the coil. This allows the mower to start.
Coil control – Here’s a different mower coil control switch. It’s a very simple connection; the contact points must separate before the coil and plug will create a spark.
The Coil (also known as Armature)
The control wire is connected from the stop/start switch on the flywheel brake assembly to the coil, which is fitted to the engine. The coil and plug won’t produce a spark so long as the control wire is connected to the ground (Metal of the engine).
A common fault is the chafing of the control wire on the engine (shorting to the ground); this effect is the same as releasing the bail lever – turns the engine off.
Check coil control wire for chafing, especially anywhere the wiring turns sharply around the engine.
Coil control wire – Coil control is a single wire with a push-on connection. Often they’ll come loose, and when they do, the mower won’t turn off.
Common Coil Faults
Coils generally work, or they don’t. Occasionally, you’ll get a coil that works when it’s cold and stops when the engine heats up. Coils are solid-state units – they can’t be repaired. Testing a coil and fitting a new one is easy; I wrote a whole post about it right here “Push mower hard to start when hot”.
Or check out the video here; it covers spark checking, diagnosing, and replacing the coil. If you need to replace the coil, check out the great deals on the Amazon link below.
Coils – Lawnmower coils give lots of problems; I replace tons of them.
Related Questions
Can a spark plug have a bad spark? Spark plugs wear out. A spark plug should be changed once every year at the start of the new season. You can check the spark plug for spark by removing it, connecting the plug wire, grounding it off the engine, and turning over the engine.
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.
Murray 309029×92 No spark, not ignition module or spark plug
Picked this up used to hopefully last me while I figure out why I can’t get the WeedeaterOne started (In another thread). Was mowing great then suddenly killed out. Wouldn’t start (acted like dead battery). Put cables on it and it turned over but wouldn’t start. Tested for spark and I get no spark with ignition module in and I do get spark when ignition module is unplugged.
The battery was unsecured and may have touched the nuts going into the rear of the engine. Would that have shorted something? What do I test from here? Any help would be greatly appreciated.
ILENGINE
Lawn Pro
check any fuses you find. Most likely nothing was hurt if they shorted, but could of killed the battery, and overloaded the charging system and cooked it. Also having spark with the ignition module unplugged indicated that something is grounding the kill circuit in the tractor. Seat switch, bare wire to ground on the kill wire. Other bad safety switched.
there were a few Murrays that wouldn’t spark if you were not on the seat, even though the engine would crank.
bertsmobile1
Lawn Royalty
Mower wiring 101 Power usually goes from the hot side of the starter solenoid. 1) through a fuse 2) the the B ( = battery) terminal on the ignition switch ( tiny numbers under the switch ) 3) to S (= Start) terminal on the switch 4) the the PTO switch or PTO safety switch on manual PTO’s 5) to the brake safety switch 6) to the trigger wire on the solenoid. This is a daisy chain so a break anywhere = no cranking If the solenoid has only 1 small wire then the ground is via the case which will benefit from a clean where it contacts the body of the mower to get a good contact.
The ignition control can either be on the key switch M G = off or on the throttle plate. follow the thin wire from the coil This is a ground wire. Ground = off Open circuit = on
Question: Getting a Murray Riding Mower To Run?
I have a Murray M15542 riding mower. We’ve replaced the starter and it ran fine a couple of times. Then it stopped running again. The fuse under the battery is good. My husband said he tried switching the safety switch wires under the seat and then it wouldn’t start.
Could there be another fuse somewhere or did that mess up the battery or something else. Please help because I’ll be the one to fix this! And I’m the one who does all the mowing.
Answers
The carburetor may be clogged. A clogged carburetor is most commonly caused by leaving fuel in the lawn mower for a long period of time. This sticky fuel can clog up the carburetor and cause the engine to stall. If the carburetor is clogged, try cleaning it with carburetor cleaner.