Picture of How to Repair a Lawn Mower Engine.
In this instructable I will show you how to repair a lawn mower engine, and how to finally kill those gremlins which have been lurching in its bowels. Of course there is now way I can tell you every single problem that could happen to your engine, so I will tell you the major parts of the engine, and how to repair them. I am not a trained mechanic. What I have learned comes from years of reading, and much trial and error. Hopefully from that I can teach you how to become more of an independent person, and maybe save you a few bucks
Remove these adsRemove these ads by Signing Up

Step 1: Disconnect the spark plug.

Picture of Disconnect the spark plug.
4 stroke 10.JPG
Before you do anything with the lawnmower you should disconnect the sparkplug. This will leave no chance of the engine starting with you working on it. It is better to loose a few second than loose a few fingers! It is also be a good idea to wear some working gloves, because engines can be very sharp and dirty which will give you an infection. Eye protection should also be worn so that gasoline and bits of metal cannot end up in you eye.

Step 2: Pre Diagnoses

Picture of Pre Diagnoses
Before you go and disassemble the whole engine it would be a good idea to first look at the spark plug. This can give you important clues about what is going on in there. The one spark plug condition that was not mentioned on the chart is the meltdown. The sparkplug will have melted metal around the gap, and is not typical but can be caused by a lack of good oil in your engine(CHANGE YOUR OIL). As long as I am talking about spark plugs I should also mention that if your spark plug gets striped you will need to buy something called a heli coli, which will patch the damage.
1-40 of 127Next »

wonderful.. I really like it...

Kilo mike4 months ago
I was mowing my lawn and hit a ant pile and my mower stalled out and wouldn't restart any suggestions on what it could be
RoseH15 months ago

Thank you for such a detailed tutorial. I appreciate the included pictures along with the explanation. Sometimes I hear the words people are saying, but I can't picture what they are talking about. Our lawn mower has been acting up lately so I'm going to run through these steps to try and get it working again.
<a href='' ></a>

I have no strength on my arms and can't pull the string hard enough to ignite the spark plug of my mower. Can the spark plug be replace with a battery clicker...? It looks to me that the only thing needed is a spark to start the engine running.... do such gadget exists....? Pardon my ignorance.... :)

I have no strength on my arms and can't pull the string hard enough to ignite the spark plug of my mower. Can the spark plug be replace with a battery clicker...? It looks to me that the only thing needed is a spark to start the engine running.... do such gadget exists....? Pardon my ignorance.... :)

The choke on my Craftsman self-propelled mower gradually shuts itself off after starting, but when it does, the engine stops. If I hold the choke lever about midway and not let it shut off all the way, the mower continues to run. Any suggestions? It's 10 years old, but I haven't run it for 4 years. It worked fine then.

Hello Bill,

Sorry a late response..But if its been sitting that long its having a hard time drawing the fuel up from the bowl of the carburetor..I suggest taking the carb. apart soaking it in a chemical carb cleaner for a couple days..Its most likely gumed up inside there like tar it will never do right until that is done.Then blow it out with air hose and a spray cleaner you should be good to go.

Thanks for the help. Running it with the choke half on for now.
Lawn Mower is a machine which is used for cutting grass in garden, lawn etc. The machine is very helpful in cutting in equal size & shape. This equipment is generally used in houses, bungalows, resorts etc to create beautiful scenery for visitors. The tool requires daily maintenance due to work properly. Here some steps are written which can help user to repair the machine. Similarly the cars should be serviced in proper service center.

The battery died on my Lawn Mower, so I put Gas in it ,I primed it to start, when the gas is used up fron primer the mower dies. what can I do/

BruceA17 months ago

Have a question on a mower..Go to and click on contact button ,ask your question and will reply as soon as possible!


Jjavaheri9 months ago

This is a great post! thanks for posting it

hokiegirl5 years ago
There is oil leaking around the engine case of my push mower and it won't start. When it does start, runs very, very rough and only for less than a minute with lots of smoke and then shuts down and cannot be started. Any ideas what might be wrong? Pam
tilt over the mower and look at the center of the blade. pull the starter cord slowly and see if the head of the bolt wobbles as it turns. If it does you have bent the crank and the engine is good for parts only.

If that's not the case, check to see if the flywheel key is partly broken. This could mess up the timing enough to cause your issues. It's a > $5 part.

Stop! Safety first! Before attemptig the above instructions it is important to first remove your spark plug. Also when you do tip your mower it is important to only tip it with the carburetor side up in the air!!!!

If the choke is off and still blowing lots of smoke. is it a 2 stroke or 4 stroke? have you cleaned the air filter any time that you have owned it or the oil for that matter. It sounds like a cylinder or head gasket to me. Its sucking in air . after piston ignition, hence all the unburnt fuel. OR It could be something so simple as a stuck float in the bottom of the carby thats giving the thing too much gas. like having lots of booze put down ya guts, its gunna hurt
too much oil, try draining the oil and replacing it with the right amount, keep checking the dipstick as your adding oil
just what I was looking for
Tbus1 year ago

This is a good learning tool to repair a lawn mower. I just purchased a repair book that has a bunch of "how to" pictures and is actually a little self-paced course with a CD. It's a nice reference tool if you ever get in a repair bind:

briggs mower wont start ,blowing oil out of muffler.any thoughts
If it is blowing oil out of the muffler it probably has a bad or broken valve which would cause it to have low compression and not start if you have a compression tester that would be a good place to start
I waited until I had a full season of use before submitting this review. My prior mower was an electric corded BD Lawn Hog that I had for six years. I'm used to being tethered to an electric cord for mowing the lawn. My property is 60' x 100' on Long Island and relatively flat. This Greenworks mower is way better than the BD I used to have. It's a bit bigger, 20" vs 19", but it's lighter, more manuverable and even though both are 12 amp, the Greenworks mower seeems to be more powerful. I always bag the clippings so I can't comment on how well it mulches. The bag mechanism is great. The spring loaded flap closes securely. The deck is metal not plastic as in the BD. The blade design is different too and I think it cuts better. I did the lawn today after not cutting for two weeks. The Greenworks cut through the high grass with ease. The price is great. It's a "green" product that doesn't pollute the air. It's quiet compared to a gas mower. The light weight makes it very easy to use. I have no complaints am I am very pleased with this product. Read more here
knowlzys1 year ago
we have spark, it was overfilled with oil and fixed this; -Briggs and Stratton- put in new petrol and now no start?
diva1911 year ago
i removed mine, can not get it back on. my problem was grandson put oil in gas tank. any suggestion.
rinse with water and soap to get the oil out (be sure to get all the soap out) then rinse with gasoline
mattyfu2 years ago
Great ible, thanks!
PaulRedd2 years ago
I signed in for the free account and I have tried three times to get this pdf and I keep getting a loop back to where I was.
adel antado2 years ago
My father told me that an ounce of prevention is worth a pound of cure. The majority of lawn mower problems relate to old gas, that is gas left in the mover at the end of last season then expected to start at rhe beginning of the next season. Gas is hydroscopic, that is it will absorbe moisture from the air. Over the winter season, any gas left in the mower will absorb enough moisture from the air to make it uncombustable. The "ounce of prevention" for lawn mowers is at the last mowing of the season is run the mower until all the gas is used. Then, open the cap of the small tank next to the carborator to let any residual gas evaporate. The mower will fire-up as new with fresh gas at the beginning of the next season. This should be done after every mowing in Florida where the humidity ruins gas in a few days.
Also, it is a good idea to change the oil before beginning to use the mower in the new season. The air filter also needsw cleaning or replacing each year. A new spark plug every year ore two is also a big help.
wrmc2 years ago
I have a Toro 1987 mower with a great aluminum base. It is still in great shape. And it is light!! My engine is shot. I would like to replace it with a new engine. The motor was a Tecumseh 4.0 hp. wit a 1" by 2" shaft. I don't find any engines with this same size shaft for sale. the closest I find is a 1 13/16 by 7/8 ". Tecumseh is no longer in business. Toro doesn't sell a new engine for it. I have found engines in this shaft size that are meant for power washers! Will they workon a lawnmower?

It appears that all small lawn mower engines have a standard attachment hole configuration in the base of the mower. That is except for Toro. It looks like the standard is rotated by 45 degrees from the engines now for sale. Is this true?

Will a new engine mounted side ways on this configuration work ok?

Can the manual start mechanism be installed so that it is in a different position so that it will come out of the new engine in the proper position to be pulled from the back of the engine?

Sounds like a lot of problems to be worked around!!!
bdaoud3 years ago
I have a problem with my lawn mower and that is when I turn it on, it releases black smoke and sputters then eventually it turns off. It has plenty of gas and I thought the problem could be because it was low on oil. I put enough oil in it but it does the same thing. Please help.
sady1991 bdaoud2 years ago
You may have too much oil in the mower
Sounds like the air/fuel mix is too rich. Check that the choke isn't on and that there are no blockages or broken parts in the carb and that the butterfly valve is turning with the throttle.
ashtiany2 years ago
I have craftsman with kawasaki FJV series engine. Problem i have after changing the spark plug, primb bulb and clean the carburator engine start right away and run run for 2 seconed and shut off. by pumping fuel via primery bulb start again and run for 2 seconed and shut off again. how can i fix my problem.
Craftsman 197CC with Kawasaki FJ180V-FS05 series motor
thak you
rsowalker2 years ago
I went to start my mower for the first time and it pulled funny and oil came out of the muffler. What do you think
sw2543 years ago
im haveing trouble with my lawnmower when i pull it and it clutters i checked the spark plug and it sparks so im not sure whats wrong any advice
notjoe93 years ago
Hello All,New guy here,having trouble with 12.5 briggs I/C motor (model 289707 / type 015401 )
it will not start,has good spark,i shot ether in back of carb. flame came out,so I am wondering does this prove that I have a timing/valve problem? or could this happen from a dirty carb?
Thank you,
rm88 notjoe93 years ago
notjoe9 - Smoke or fire tends to be indicative of burning oil. As far as general Briggs engine troubleshooting, they have a page about the reasons why engines do that and a few possible causes. Check out their FAQ:
Racer2313 years ago
Im trying to learn how to build one so i can fix one please teach me how to build the engine. i dont know wats up with my engine so i wanna take the newer parts and build a new one.
ichevez3 years ago
Richard,  if you are still having trouble fixing the small engine, there is a great shop in Baltimore where they fix all kind of small  diesel and gas engines. This is the link to their website: Small engine repair.

Great article btw, let me know if you have any other questions.
1-40 of 127Next »