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How to Repair a Lawn Mower Engine.

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
 
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Step 1Disconnect the spark plug.

Disconnect the spark plug.
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.
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102 comments
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May 16, 2012. 7:46 AMashtiany says:
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
Apr 2, 2012. 5:31 PMrsowalker says:
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
Mar 24, 2012. 2:25 PMsw254 says:
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
Sep 22, 2011. 4:05 AMnotjoe9 says:
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,
Mar 20, 2012. 1:21 PMrm88 says:
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: http://www.briggsandstratton.com/support/frequently-asked-questions/engine-emits-white-blue-smoke-while-running/
Jan 4, 2012. 2:42 PMRacer231 says:
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.
Nov 29, 2011. 7:21 AMichevez says:
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.
Apr 26, 2011. 5:46 PMbdaoud says:
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.
Jul 29, 2011. 5:07 PMmaster key says:
what kind f motor is it
a Briggs and Stratton
Classic, Sprint, Quattro or a Quantum
or is it a Tecumseh
May 2, 2011. 11:22 PMWeegee097 says:
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.
Mar 28, 2010. 8:40 PM34638Fred says:
 I have a 6.5 h.p. briggs that i can pump the bulb 3 or 4 times and the engine will start but shut off immediately. It sounds like it runs out of gas. but when i take the carb apart the bowl is full and the float moves freely. It seems to be a carb problem to me. I have taken the carb off and filled it with carb cleaner and blown it out with air. It has a brand new air filter and new gas. Can anyone shed some light to what might be the problem. Any comments will be appreciated 
Nov 17, 2010. 12:17 PMjcmssmallengines says:
i think your injecters are stop up try clening them out
Jul 29, 2011. 5:03 PMmaster key says:
There are no injectors in a lawn mower engine
May 27, 2010. 7:47 AMkill-a-watt says:
A quick test would be to

!. take the air cleaner off (but return the bolt to the hole, and screw the bolt in part way.

2. start the engine after priming per normal

3. give it a shot of starting fluid or WD-40 down the throat of the carb, if you can keep it going with a spray bottle, then you have a fuel problem and can rule out ignition or timing issues

I'm guessing you either need to re-clean the carb or there is debris in the fuel tank that block off the fuel after it it gets started.

Does the bulb return to "inflated" as soon as you release it, or is it a little slow?
Nov 15, 2010. 6:42 AMkill-a-watt says:
Someone PM me about this comment and I thought I'd share my reply.

>>You asked if the re-inflate bulb on a briggs & straton engine was slow to reinflate. That is happening to me and I'm guessing it is from restricted air flow into the carb.

remove the air cleaner, spray with carb cleaner, reassemble at least the center bolt that holds the air-cleaner on (important for many engines). Do a $1.98 tune-up - This is detailed by me in the comments here:

http://www.instructables.com/id/How-to-Clean-Motorcycle-Carburetors/ I

n your case, you'll need to prime, start the engine, and slap your hand over the air intake before the engine dies due to lack of fuel. You might be able to quickly remove your hand and spray into the air intake some carb cleaner or wd-40. to keep it going. It sounds to me like you have a fuel delivery problem. You can verify it's the fuel by starting it and keeping it going with sprays from wd-40 down the carb throat.

I'd also check and see if there's anything in the fuel tank, and wash it out if need be. If there's a fuel filter, it may be worth trying to replace it.

Dave Rock has quite a few videos on small engines. Try going to

http://www.youtube.com/profile?user=Davidsfarm#g/u

and then use the search box with the term "briggs" to tease out the good stuff from all the track racing and car jumping vids. Good luck.
May 14, 2010. 1:54 PMraychwv says:
I have the exact same engine and same problem. I checked my carb. and it was dirty, cleaned it and still nothing. The magneto is probably the culprit, but I am not positive how to check it. I t shows a short with and ohm meter when I touch the ground wire and the engine. Any idea? thanks

Mar 31, 2010. 10:33 PMnickspm says:
Fred,

If you haven't tried this, take out the main jet ( doubles as a screw) that unscrews when you remove the bowl.  Then get a little wire and push it through the top and the bottom of the jet as well as the little holes on the sides.  When the jets get clogged, the mower can't breathe.
May 8, 2011. 10:20 AMVidDroog says:
When the jets get clogged....fuel cannot be sucked in and sprayed into the fast moving air stream (low pressure Bernoulli effect at the jet opening into the venturi/throat) of the carburetor; ... Over winter, water condenses from humidity in the fuel tank with cycles of temperature changes...denser than fuel it sinks to the bottom and is then first to head to the carburetor's float bowl; corrosion ensues in the tank....and in the float bowl if not old fashioned glass (which was glass for a reason--see water and debris for easy removal); additionally with aluminum allow float bowls, the corrosion is somewhat chalky and can be sucked in and wedge in the jet (as well as the steel gas tanks iron oxide/rust grit); not to mention the dissimilar metal potential for electro-chemical corrosion.... careful with the wire, jet precision size determines flow, hence different number/size jets for elevation and engine/carburetor flow capacity; copper wire from multi-strand electrical wire/lamp cord will often be small enough, and fairly soft...

if your lucky it is just water to empty from the float bowl: water and/or corrosion debris, is the common reason for brief run and shut down, after squirting a bit of fuel through the spark plug hole before replacing spark plug (after have checked for such a bit of debris or carbon in the spark gap, and if spark to check magneto)

And for electrical, just lay the spark plug (connected with the spark plug wire) on the engine fins (for ground connection), pull the starter rope and look for the spark..
May 8, 2011. 6:52 PMKJ6EPL says:
I would also like to add that another problem that makes the engine hard to start or not want to run at all is a worn out carburetor bowl gasket. It will drain your gas tank quickly too as gas will evaporate out of the carb. Sometimes gunk can help seal up an aging gasket to the point where the gasket will not seal once cleaned. To test for this, with the engine COLD and OFF (if it's hot/warmed up a fire may result), connect the carb to the gas tank and allow the bowl to fill. Tilt the engine slightly. If gas spills out of the carb bowl, replace the gasket.
Apr 22, 2011. 7:17 AMBeach63 says:
I have a Murry lawnmower with a Techunsia 4.4hp engine. It starts for about 2 seconds then cuts off. Anyine have any ideas?
Mar 3, 2011. 11:57 AMmaro-1 says:
this is my first time working with an engine so this really helped me out. thanx : )
Sep 24, 2009. 5:12 AMhokiegirl says:
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
Sep 3, 2010. 4:53 AMwaz444 says:
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
May 27, 2010. 8:01 AMkill-a-watt says:
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.
Mar 3, 2010. 6:33 AMphoenixxxx says:
too much oil, try draining the oil and replacing it with the right amount, keep checking the dipstick as your adding oil
Jul 4, 2008. 11:25 AMriverside says:
What is considered adequate compression on a self propelled push mower. Engine will not start. I measured compression by slowly turning pulley by hand and only got 15 lbs. Will a small engine like this run on this amount of compression? What is normal. I can't seem to find this answer anywhere. All articles and manuals seem to avoid this. Lee
Sep 3, 2010. 4:21 AMwaz444 says:
to measure the compression of any small motor is to insert compression test gauge, pull the starter a couple of times, normally only 3 to get the good stuff. hold for 15 seconds then release the pressure. normally for a 2 stroke mower 125psi. anything under that you may want to check your piston rings and maybe the barell for scoring
Aug 25, 2010. 5:28 PMLetsExplodeSomething says:
100 psi is normal
May 27, 2010. 7:57 AMkill-a-watt says:
If you hit a rock, you could have partly sheared the flywheel key. that could give you low compression.
Mar 3, 2010. 6:42 AMphoenixxxx says:
internal damage don't waste your time scrap it!!
Dec 29, 2008. 10:41 AMstoobers says:
80 psi. Google search for "tecumseh engine compression" Some books will say 60 psi minimum. I am guessing the engine will not run on 15 psi. But maybe your engine has a "compression release" that is lowering compression for easier starting. Try pulling the plug, then squirt sae 30 oil in the cylinder (normal old motor oil.) Work the piston up and down a few times. Then do a compression test. If the compression jumps up, you have worn out rings (or valves, if it is a flat-head.) I've had new tecumseh engines start on the second or third pull, even after long storage. They should never be hard to start. Also try a 2 second puff of starter fluid, onto the OUTSIDE of the air filter. The engine should kick over immediately! If it doesn't you might have a bad spark.
Sep 2, 2010. 8:11 AMrobinfelton says:
My lawn mmower seems to run at half speed. I can manually speed it up by moving the throttle linkage, but when it runs on it's on, it runs at only half speed and kinda eratic as if running out of gas. It was running fine, shut it off, came back in 5 mins and it started running this way. I have changed the gas in the tank, checked the fuel flow and cleaned the carburator...anybody have any ideas as to what is wrong?
Sep 3, 2010. 4:13 AMwaz444 says:
Blowing lots of smoke??? did you turn the choke off?
Jul 30, 2010. 2:02 PMsherri lynn carltn patterson says:
I appreciate this as a women I need all the help I can get and you have help me alot.
Jun 3, 2010. 5:56 AMTroubledMower says:
Good Day Folks,

My Murray 6.5hp mower won't start, gas tank has a small crack, bought a new spark plug but still nothing. Have good rotation when pulling thelever to start the mower. Thx for any help.
Jun 1, 2010. 10:14 PMdenleep says:
Very informative thank you. I have been through numerous web sights and this by far has been the most helpful!!!   

                                                                         THANKS AGAIN    Denny
May 30, 2010. 6:39 PMIW5 Industries says:
I recently scavenged an ariens push mower with a 6.5 horsepower kohler engine in a lawnmower dump I recently discovered. The mower was wet and covered in mud and dirt from sitting there but started right up on the first time! thank you kohler!
May 27, 2010. 7:41 AMkill-a-watt says:
removing the nut for the flywheel is a great application for an air impact wrench, if available.
May 27, 2010. 7:39 AMkill-a-watt says:
to be extra safe, I'll either remove the spark plug, or put a piece of rubber hose over the end. 

Just pulling the wire could leave the wire close enough to jump the gap.

I've been told to always remove the spark plug with a snow blower, as the stored compressed air can be enough to shear off a finger if you clear the obstruction that is jamming up the blade.
May 27, 2010. 7:22 AMkill-a-watt says:
I feel a strange disturbance in the Force, much like this instructable is about to be "featured" on the front page.
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