Lawn mower no compression. Here’s What To Do If Your Lawn Mower Won’t Start

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.

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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.

lawn, mower, compression, here, your

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lawn, mower, compression, here, your

Check for Debris in the Mower Deck

Grass clippings can get clogged in the mower deck, which can prevent the blade from turning. This is a common problem if you’ve cut wet grass or let the lawn get especially long and bushy between cuttings. If the cord is hard to pull, that’s a good sign that there’s debris clogging up your mower’s deck.

This is a pretty easy problem to solve. With the mower off, flip it on its side or upside down and scrape out the gummed up grass clippings. Once that’s done, you can flip it back over and start it up again.

JJ Gouin/Getty Images

Check the Air Filter

The lawn mower’s carburetor regulates the mix of gasoline and air going into the engine where it’s burned to create power. Before air goes into the carburetor it passes through the air filter which prevents dirt and debris from getting into it.

If the air filer is clogged or dirty, it throws the ratio out of whack. Sometimes that results in your lawn mower smoking, and sometimes it prevents it from starting entirely. So take a look at the air filter to see if it’s dirty. If so, you can clean it or just change it outright.

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Check the Carburetor

Another common reason for a lawn mower that won’t start is a clogged or dirty carburetor. It can also cause your mower to run rough or spew black smoke when you’re trying to cut the grass. If that’s the case, you may need to clean the carburetor.

To get to the carburetor, you’ll have to remove the air filter. Once that’s out of the way, you can remove the carburetor in order to clean it.

Once it’s out, check for corrosion. If you see chalky/powdery white corrosion like this, it’s probably better just to replace it. To clean it, take it apart and spray carburetor cleaner on the parts and inside the housing. After that, put the carburetor back together and reinstall it in the mower.

Check the Fuel Filter

Like the air filter, the fuel filter prevents dirt and debris from getting into the combustion chamber of your lawn mower’s engine, taking that stuff out before the gas gets mixed with air in the carburetor. Problems with the fuel filter might also result in the engine sputtering or rough idling, even before it gets to the point of preventing the mower from starting.

To start, tap the side of the carburetor to help the flow of gas. If that doesn’t work, you might have a clogged filter.

Not all lawn mowers have a fuel filter, but for the ones that do, it’s usually located in the fuel line or the fuel tank. To find out where the fuel filter is at, check your lawn mower’s owners manual, which will also tell you what type of filter it is.

If the filter is in the fuel tank, you’ll need to drain the gas from the mower into a drain pan, assuming you can’t run the engine until it’s out of gas. If the filter is in the fuel line, clamp off the fuel line before removing the filter. Once you have the filter off, you can check to see if it’s dirty and clogged by holding it up the light. If it is, install a new one. Make sure it works with this lawn mower maintenance checklist.

Lawn Mower Repair Tips – A Self-help Guide

Like any machine, every lawn mower needs regular maintenance. Without regular maintenance, the chances of problems developing increases significantly as time goes by.

In today’s modern world, we all get busy from time to time. Perhaps you’ve missed a service or two and now your lawn mower is showing early warning signs that it is in need of repair. If you are having problems with your lawn mower, for any reason, we hope this guide helps to point you in the right direction.

Briggs & Stratton No Start Won’t Turn Over Hydro Lock Compression Release Valve Adjustment Easy DIY

It is worth noting that, depending on the make and model of your lawn mower, the steps and information contained within this article may not be consistent with your lawn mower. This article is intended as a general guide only. It is recommended to seek professional service assistance from a qualified repairer if you suspect your lawn mower is in need of repairs.

Lawn Mower Uses Excessive Fuel

If you feel that your lawn mower is using more fuel than normal, start by checking common service items. Inspect your air filter to ensure it is not blocked, and replace it if needed. Check and replace your spark plug, as a poor quality spark could lead to incomplete combustion. Check to make sure there is nothing caught up under the cutting deck which may place drag on the motor. And lastly, check and replace your mower blades if they are dull. A fresh set of mower blades will mean you won’t have to run the engine at high RPM to achieve the same cut.

Next, check the float level in the carburettor to make sure it is not sticking open and is correctly adjusted following your service manual. After that, check the high-speed governor setting and then check that the choke plate is fully open when the engine is running. If the choke plate is in good order, check the pilot screw and adjust it as per your service manual to ensure your air/fuel ratios are within specification.

If you still suspect your lawn mower is consuming more fuel than it used to, check the engine’s compression. If the cylinder compression pressure is low (refer to your service manual for test procedures and specifications), first, check to ensure that the valve timing and clearances are set correctly. Other checks will include ensuring the valve and springs (4 stroke engine) are not sticking open or damaged. And inspecting the cylinder bore for scoring with an inspection camera.

Lawn Mower Engine Hard to Start

Petrol mowers have several reasons why they won’t start, with a common one being the spark plug. If the spark plug is not firing, then there is no way to ignite the fuel to fire up the engine. Remove the spark plug and give it a clean to remove any built-up carbon and check the gap is set correctly. If it has not been replaced recently, replace it with the recommended spark plug for your mower.

Next, remove and replace your fuel filter in case it is blocked. While your lawn mower may have a full tank of fuel, it could have been left too long or is not the correct type to use with your mower engine. Empty the fuel from the tank and check the intake system, also check the air filter. You should also top up your oil level before starting it up.

Check that the choke plate closes completely when you engage the choke. If the choke plate does not close completely, then adjust it so it does. If the choke plate is already completely closed, then check that you’re getting spark to your spark plug. If the spark is working as expected, then check the compression as per your owner manual. If all is well with the compression, check for a sheared flywheel key. If the compression is not within specification, then you will need to inspect the valve settings, cylinder bore and piston rings.

Lawn Mower Burning Excessive Oil

Common causes of burning oil include over filling the sump with too much oil (4 stroke), too much oil mixed into the fuel (2-stroke), or a leaking cylinder gasket.

Start by cleaning any excess oil from the engine and surrounding parts, then start the engine and try to isolate if the oil is leaking from the engine itself, or being blown out of the exhaust. An oil leak dripping down the outside of the motor indicates a leaking gasket, and oil blowing out of the exhaust when the engine is running indicates an internal issue or poor fuel mix.

If your mower is 2 stroke, start by draining the fuel and refilling the tank with fresh fuel of the correct mix. If your mower is 4 stroke, check to ensure the oil level is at the right level, and not overfilled. If you aren’t sure, drain and replace the engine oil with the correct grade of oil to the full or high mark on the dipstick, following your service manual. Then if the smoke persists, investigate the breather tube from the crankcase to ensure it is not blocked, and also ensure that the cutting blades are free from excessive debris. If you find that a gasket is leaking, it is recommended to have your mower inspected and repaired by a qualified repairer.

If you have an electric lawn mower that is smoking, then the motor is most likely overheating. The most common cause of this is when the mower is used to cut long grass or particularly dense foliage, or a fault with the battery or motor itself. If you notice smoke coming from your electric lawn mower, turn the power off immediately and allow it to cool down, and get it inspected and repaired by a certified repairer. Do not attempt to repair any battery power tool.

Lawn Mower Low On Power

If your mower keeps cutting out when you are using it or feels down on power, then there are a few easy things to look for.

The first is to check the regular service items. Check the air filter is not blocked as this can prevent air from reaching the engine. Check and replace the fuel filter to ensure it isn’t blocked. And inspect and replace the spark plug. Once you have checked and cleaned your filters, move on to inspecting the blades to make sure they are not being compromised by excessive grass clippings, twigs, and stones.

You will want to ensure the RPM and governor settings are correct, too. If your engine is overheating, check the air inlet filter for any built-up debris. Remove the filter cover and housing and then clean out any dirt or debris in the filter and cylinder cooling fan areas. If your engine is not overheating then check that your oil levels are sufficient and that the oil pressure levels are as per your service manual.

Next, check that your fuel is not contaminated and that the carburettor is not blocked. Drain and refresh your fuel. Clean out the fuel lines. Then remove the carburettor fuel bowl cover and check that the float is correctly adjusted and can open and close freely. Finally, give the carby a good clean with carburettor cleaner, ensuring the jets are not blocked with debris. Most manufacturers will offer a fuel service kit to make this job easier.

Lawn Mower Is Backfiring or Popping

If your lawn mower backfires, it is an indication that your engine is firing at the incorrect time in the engine cycle. This could be due to incorrect ignition timing, perhaps the engine is ‘running on’, or you have an exhaust leak.

Start by checking the easy things, like the exhaust manifold bolts and carburettor are correctly torqued. If they are okay, then move on to check that there are no leaks on the head gaskets and that the head bolts are tight.

Next, check your ignition timing following the instructions in your service manual. This can be tricky so if this sounds beyond your abilities, it’s best to take it to a qualified repairer.

If the backfiring is limited to when you shut off power to the lawn mower, then take a look at your throttle plate. If it is completely closed, then adjust the idle speed of the engine as per the engine manual. Backfiring can also occur due to rich or lean fuel mixtures. Close the choke slightly and listen to your engine. If it runs smoother, the carburettor may need to be cleaned. If it runs rough, then use your service manual to check the compression.

Lawn Mower Starter Rope Is Sticking or Stuck

If your starter rope is refusing to move when pulled or only coming out part way before jamming, then there are several different causes that could be responsible.

Starter Cord is Crossed – When the cord retracts, it may end up crossing over itself causing a tight bond on the tightly wound cord. This can prevent the cord from moving and pulling at it only serves to tighten its grip. You need to remove the cord cover and manually unwind it until the crossed over part has been removed. Once you refit the cover, it should operate like normal.

Mower Blade – If the mower blade won’t spin freely, then the pull cord may not budge. The first thing to do is check for debris that may be preventing the blade from spinning. If this is all clear, then you will need to look closer and see if the blades are bent or damaged. If the blade is damaged, replace them and ensure the mower spins freely, following the procedure in your service manual.

Hydraulic Lock – This may occur if the combustion chamber becomes clogged with oil or fuel. The resulting effect is that the cable locks itself down and becomes impossible to move. You can check if this is the case by removing the spark plug, then pulling on the core again. If it move freely and oil/fuel spits out of the spark plug hole; you know you have found the problem.

If you have tried the above fixes to no avail, then it may be time to take it for a service at your local service centre. While there are options available for self-repair, lawn mowers can become dangerous if you don’t know what you are doing. In the case of tools with blades, combustible fuels, and electrical components it is better to be safe than sorry, and always seek the assistance of a qualified repairer.


Rislone Compression Repair with Ring Seal is a concentrated proprietary blend of high-shear and premium polymers developed for higher kilometre engines that are suffering from decreased or uneven compression. Low compression can be caused by normal engine wear and decreased sealing between the piston rings and cylinder walls. The non-dispersant olefin copolymers fill scratches grooves in cylinder walls to increase and stabilize compression in all cylinders. Compression Repair renews worn engines, rebuilds compression, restores lost power and repairs engine blow-by. In addition, Compression Repair helps vehicles pass emission tests.

Some signs of decreased compression include loss of power, poor fuel mileage, oil consumption, blue smoke from exhaust, plug fouling and engine noise or vibration. The Viscosity Improve (VI) is designed specifically to provide an optimum balance of shear stability and thickening efficiency required in old and modern engines. This performance additive meets the most severe passenger car and truck engine requirements.

Product works by freeing sticky rings and filling gaps scratches in cylinder walls, eliminating blow-by and compression loss while also reducing friction and wear. Blow-by is usually caused by gaps in internal engine parts resulting from excess wear.

Rislone Compression Repair with Ring Seal does not contain any harmful lead or other metals that could damage the inside of your engine or be burned and contaminate emissions components and the environment.

DOSAGE:For larger systems use 1 bottle for every 4.7 L of capacity. On 4-stroke ATV, Motorcycle and small engines, including wet clutch applications, use approximately 88mL per 946mL of capacity.

DIRECTIONS: Add entire bottle of Compression Repair With Ring Seal to engine crankcase at or between oil changes. Do not overfill. Results will either be immediate or noticeable within a few days of driving.

Install Compression Repair every 10,000 kilometres or with every oil change.

COMPATIBILITY:Rislone High Kilometre Compression Repair is compatible with ALL 4, 5, 6, 8 and 10 cylinder petrol, diesel and LPG vehicles, including turbocharged engines.

Rislone Compression Repair can be used in 4-cycle (4-stroke) ATV’s and motorcycles with a wet clutch since the product does not use any friction modifiers, which could potentially make the clutches slip. Use approximately 93mL per 1L of engine oil capacity.

Works with conventional, high kilometre and synthetic engine oil.

Rislone High Kilometre Compression Repair is compatible with Rislone Engine Treatment, Rislone Engine Oil Stop Leak and Rislone Rear Main Seal Repair and Rislone Nano Prime.

NOTE:If you are unsure what other additives could be in the oil system prior to adding Rislone, it is recommended to flush the system first.

Not suitable for use in Rotary (Wankel) Engines.


What are the most common causes of low engine compression?Low compression can be caused by normal engine wear and decreased sealing between the piston rings and cylinder walls. This can be the result of scratches in the cylinder walls or sticking rings in the pistons which allow compression to move from the top of the cylinder down into the crankcase below the piston.

What are the signs of decreased compression?Some signs of decreased compression include loss of power, poor fuel mileage, oil consumption, blue smoke from the exhaust, plug fouling and engine noise or vibrations.

What is Rislone Compression Repair with Ring Seal?Rislone Compression Repair with Ring Seal is a concentrated proprietary blend of petroleum additives developed for higher mileage engines that are suffering from decreased or uneven compression. It contains a unique engine additive that repairs worn-out areas in the cylinder wall thereby restoring cylinder compression and improving engine performance to nearly new original condition.

How does Rislone Compression Repair with Ring Seal work?Rislone Compression Repair with Ring Seal works two ways to solve low compression problems. First, chemical polymers work to fill in scratches and grooves in cylinder walls caused by normal wear, age and high mileage. Secondly, frees sticking rings in piston grooves to allow the rings to properly seal increasing compression.

Will Rislone work in synthetic oil?Yes, Rislone works with all petroleum-based motor oils including conventional, high kilometre and synthetic formulas.

Can I use Rislone Compression Repair in my diesel engine?Yes, it is compatible with both petrol and diesel engines.

How often should I use it?For best results, install Compression Repair every 9,600Km or with every oil change.

Can I use Rislone Compression Repair to mix with petrol in my 2-cycle (Two-Stroke) Engine?No, Rislone Compression Repair is designed to only be used with conventional 4 stroke engines.

Can Rislone Compression Repair be used in small engines like lawn mowers and tractors?Yes, Rislone Compression Repair can be used in all types of 4-cycle (four-stroke) engines. Use approximately 88mL of Rislone Compression Repair per 946mL of engine capacity. Most small engines hold around 946mL of oil.

Can Rislone Compression Repair be used in 4-cycle ATV and Motorcycle engines with a wet clutch?Yes, Rislone Compression Repair can be used in 4-cycle (4-stroke) ATV’s and Motorcycles with a wet clutch since the product does not use any friction modifiers which could potentially make the clutches slip. Use approximately 88mL of Rislone Compression Repair per 946mL of engine capacity.

Can Rislone Compression Repair be used in turbo charged engines?Yes, Rislone Compression Repair can be used in all normally aspirated and turbo charged engines.

Does Rislone Compression Repair work in all 4, 6 and 8 cylinder engines?Yes, Rislone Compression Repair works in all engine sizes. Some companies sell different size bottles for different size engines, which is only for marketing. In fact most engines have the same exact oil capacity whether it is a 4 cylinder or 8 cylinder does not matter.

Customer Feedback

I was about to sell my old Honda CRV due to massive amounts of smoke and rough idle, I had a fresh oil change and it got worse, I looked for anything and found your product in my local parts store ‘supercheap’ and thought it cant hurt. I put the whole bottle in and went for a drive around 3 hours, still smoking a small amount but after 3 days now no smoke and the idle is perfect! Some how it has more power and my fuel usage is much better. Not sure if your product is witchcraft or what but MY GOD DOES IT WORK.

How to fix a mower with no compression

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What Happens If You Run A Lawn Mower Without Oil

It’s common knowledge that the moving parts of a machine need oil for lubrication to function effectively. However, you could find yourself in odd situations where oil gets depleted in your lawn mower while in use.

Sometimes this will happen without your knowledge catching you by surprise. Read the rest of the article to know what happens if you run a lawn mower without oil.

Can A Lawn Mower Engine Run Without Oil?

No, a lawn mower engine cannot run without oil. If you try to run it this way, you’re effectively killing it by damaging the engine parts beyond repair.

Whether your lawn mower engine is two or four-stroke, it requires oil during operation to smoothen the moving parts such as the crankshaft, the piston, and metal bearings.

Also, with oil, there is less friction— the temperature of the internal engine components remains at normal levels preventing the engine from overheating.


Several mechanical issues could arise if your lawn mower engine runs without oil. Typical signs include:

Other signs include loud knocking or rumbling sounds coming from the engine.

Your lawn mower engine will seize if it runs without oil longer, ultimately failing. The major culprit is the increased friction leading to overheating.

Substantial damage occurs to the metal parts causing small pieces to chip away. The other problem you’re staring at is poor lubrication leading to the crankshaft and pistons interlocking with other metal parts.

Additionally, you have to deal with the premature wearing of the piston rings, potentially resulting in low compression levels.

lawn, mower, compression, here, your

How Long Will A Lawn Mower Engine Run Without Oil?

As per various manufacturers, a lawn mower engine shouldn’t operate without oil. However, there could be scenarios where your engine runs short of oil during operation.

Different lawn mowers vary in their reaction to an oil shortage.

For the record, a two-minute oil shortage during use is enough to cause permanent damage to the engine. However, this is not cast in stone since some engines may still have room for repairs.

The parts that take the most beating with visible damage include the crankshaft, the piston, and the bearings.

How Do You Know When A Lawn Mower Needs Oil?

As already highlighted, oil is a vital component of your lawn mower engine to ensure its functionally operational.

However, too much oil is equally bad for your engine and is a major cause of leaks and hydro locking.

You should check the oil in your mower when the mower is parked on a level surface, and the engine is off.

The dipstick is usually found on the side of the engine. It has two marks; the top mark indicates a full oil level while the bottom mark indicates low oil levels.

The oil is at critically low levels below the lower mark.

Tip: Always turn the dipstick anticlockwise when removing it from the engine.

How To Correctly Add Oil To The Lawn Mower?

Once you’ve checked the oil levels in your engine and determined that the amount is insufficient, proceed with the steps below.

Given the small nature of some dipstick tubes, you may need to use a funnel for proper filling.

Add a little oil as you recheck the oil level. Keep adding and rechecking until the upper mark is reached.

Avoid the temptation to overfill beyond the upper mark.

What Should You Do If You Accidentally Start Your Lawn Mower Without Oil?

If you accidentally start your mower without oil, the first thing to do is to stop it immediately. Look at the below scenarios to assess the damage caused:

Scenario 1: The piston is still moving slowly.

There is a considerable chance your mower engine can roar back to life.

Scenario 2: The pistons and other parts are welded together.

There is little you can do about it.

If the former situation occurs, check the user’s manual for guidance on how to fix it. If that doesn’t seem to work out, you’re better off enlisting the services of a technician.