Fix a Lawn Mower that Will Not Start When Hot - How to Diagnose & Repair 

Great video, I just went through dealing with a Briggs 725EXI lawn mower engine that always starts and runs great for as long as you want, but is dead as a dodo immediately after you shut it down even for a couple of minutes while emptying the bag. And then after about twenty minutes of cooling down, starts right up again. Replaced the coil, cleaned the carb, which helped a little for a while, and then replaced the carburetor the other day, and the problem still persisted! I had an AH-HA moment yesterday when I started to suspect that crankcase breather oil fumes that dump into the air cleaner were involved. Sure enough, after temporarily disconnecting the breather hose from the air cleaner housing, the hot start problem was eliminated! Did repeated hot starts on the first or second pull. This 725EXI has recently starting to burn a bit of oil, and you can see oil sludge building up inside the air cleaner housing at the carb inlet. Apparently the hot oil fumes are messing up the fuel mixture enough to prevent a hot start, but do not really impact a running engine, the engine always runs very strong and smooth as long as you let it after a cold start, but once hot, nothing doing! The whole situation makes sense now, once the engine has cooled down, the crankcase fumes are not present on a cold start to mess up the air fuel mixture…. I’m posting this to bring this to everyone’s attention, I have not seen anyone else make the connection of the hot no start problem to crankcase oil fumes. Looks like the engine needs a piston ring job, wonder how easy that will be, anyone out there have any experience with that? Any associated RU-vid videos? Chris B. Stonington CT

Exact lawnmower, exact problem since new. Took to a toro dealership said they fixed it. 2nd time I used it, it acted up again. I sold it yesterday they found your video and took off the carb and cleaned it. Solved the problem.

Same issues I had. I first replaced Spark Plug & Air Filter, didn't do any better. Cheaned fuel line, carb & stuck auto choke.👍 Fixed.😃

I was wondering if maybe it was a choke problem or if the gas cap had a venting issue instead of the coil. You figured it out so good job. The video is very well done and thanks for sharing with all of us.

Brilliant video. I stripped the whole fuel system down and it still struggled to get going. After watching this I cleaned out the carburetor😁 and used Engine Starter Fluid. Works perfect now. THANK YOU

Yup, went through the same thing myself. I solved mine with Sea Foam in the gas. I know, now days everybody poo poos Sea Foam but it works for me. Great video.

I have the exact same problem. If engine is hot and I restart in about a minute or less - no problem. Somewhere around 3 to 4 minutes off, it won't start. I suspected hot engine auto-choke issue but didn't want to waste time until I saw this video. THANKS! - to author and others. Will try carb and fuel line clean out, replacing gas cap.

This is EXACTLY what mine (10 years old) is doing. It's slowly been getting harder to start (and had always started on the first pull) over the past month. I am going to clean the carb and jet and see if that takes care of it. It's been a fantastic mower until now.

I have a rock solid Husquevarna with a B&S engine on it. It starts first pull *every* single time for all 6 years that I've owned it. *Except....* it sometimes won't restart until it cools down JUST LIKE THIS ONE!! I can't wait to go home and see if I can fix it for good!! I'm sooo tired of having to mow my lawn in chunks day after day. Thank you good sir!

12:21 that victory cheer, that was such wholesome goodness. Much respects, now time to follow your lead and get my mower back to working.

Yay. Congrats! This is NOT the prob with mower, but it IS a prob with my 30yo Ford Fiesta: starts first time in the morning but when I come out of the supermarket it can take up to ten tries before it starts. You can hear the starter whine and finally connect. Did a bench test on starter, cleaned all connections, no difference.

Thank you for going step by step. It's put things into perspective of how I can track down issues. I think mine is having an ignition coil problem, but your will help me narrow it down.

My Toro Turfmaster had the same issue. Was the ignition coil. I learned never to shut it off while mowing, emptying bag.

I ve been fixing mower s for some years and In my experience its almost always the carb. hardly ever a coil or plug. BUT I h ave one now that still wont start hot even with a clean carb... seems to need a bit of choke even when hot. driving me crazy. All the best!

I have EXACTLY the same issue with my mower. I'm going to try cleaning the carburetor. Thanks!

Your old plug had spark so why would you question it? Great video, by the way.

My Troy Bilt does that same thing, has done it since it was new. I think it's because of the easy start automatic choke. I think it chokes it even though it's hot causing it bot to start

WOW!!!! THANK YOU!!!! i'm trying that tomorrow!!!!

Awesome information. That is exactly what my mower is doing. Thank you.

I've got a Stihl FS 280 Brushcutter that does exactly the same . Starts and runs a treat but once it's heated up , if you switch it off before you're done , then you can forget starting it again . Now I know a good place to start . Thanks .

"Throwout bearing"!! I've never hear if them. Thanks a lot for the clue. I shall start searching forthwith. In fact I bought a second hand starter from Napar (is that the word?) for 60€ but never got 'round to testing it for the simple reason I didn't know how😮. Well, I finally tested it and the pinion/bendix shot out but didn't spin. Dismounted my one and it did shoot out and spin so having cleaned all connections I put it back -- no difference. Someone said if the starter isn't used for a long time (9 months since I bought it) it can stick. So I'm looking up how to clean them up, and now also "throwout bearings'. Thanks again for the lead! Very kind.

I am having this issue with the same kind of mower just wanted to see what your fix was. After disassembling the top of the motor checking and rechecking the coil gap and making sure the choke flapper was operating correctly. I found that the thermostat the that keeps the choke open when it's warm is causing the carburetor to not deliver fuel to restart. Therefore I need to clean the carb like you did. So there's the root of the problem, the choke system!

I have the exact same problem. Marvelous.

Nice fix. It was water in the gas. Just pour the gas out in a clear jug you can see the water inside. Then drain the gas from the carburetor bowl by removing the bowl plug.. Before you do all that above You can tilt the mower towards the carburetor to see if it starts. Thats how I find out. 13:35

the easiest fix is a shoestring tied around the handle. NEVER shut it off!!

I have a Husqvarna self-propelled with a Honda engine that will start on 1 or 2 pulls even after sitting in storage. It has never given me any problems. My Troybilt Pressure Washer uses a Briggs, and it will no-start after getting hot. In fact, it exhibited this problem even when new, and after carb replacement. I guess it’s time for a coil replacement.

Check coil and Flywheel. Believe it or not you can hit something and jam the flywheel. I replaced both. Have new mower now.

Thanks for this. My dad's mower is doing this. The same exact mower. I have to use the electric start and it won't start after shuttting it off to get to the front lawn. My dad is no longer with us so he can't help me.

TYSVM!! Watching & listening it felt like you were recreating moments to myself in the yard working on various things. "That's odd...." "This is a unique problem...." 🤣🤣🤣😁

You did great ,I had a similar problem ,I just go it fixed

Thanks chief!!! Hope to do a Happy dance too after cleaning my fuel system thoroughly. From the tank, inlet hose and all of the carburetor😁

I was 99% certain what the problem was before I watched very much of your video? Wanted to see if there was something I had not seen, but that did not happen. It is the main jet that anchors the bowl to the bottom of the carburetor, and that's what it always is! That jet gets plugged very easily. I am going to install an inline fuel filter between the tank and the carb and see if that eliminates the non-starts.

Great video! I been having the same issue. I thought it was just me and I was just stupid.

good info, I tried this and I still have issues. it seems to loose compression when hot, suspect exhaust value issue. it is also on a Toro. I even replaced the carb with a new one. I had a used Coil that was known to be good and tried that and still have same issues so I knew its not a coil

if its hot and it wont start with starting fluid...you dont have enough spark to start it....change the coil. I've seen these things go bad...sometimes in the middle of cutting it'll just stop...you let it cool down and it will start right back up. Like someone else said spark plugs rarely go bad...you can pull and clean them, check the gap (about .030 for Briggs) and ensure insulator is not cracked..and torgue them properly. they need to be tight enough to seal properly.

I have a ST100 bush mower with this exact issue. it doesn't restart when the auto choke system opens the choke butterfly valve in the carb. This however is the correct function of auto choke as restarting a warm engine choked may flood it.... as a closed choke creates the maximum gas draw. Choke is needed when cold but should be open when warm. if a mower experiences this issue and a jet of fluid starts it, I guess there may be a suction leak somewhere resulting in no fuel delivery when the mower is manually pull stated. To complicate everything mine has a evap filter, additional hoses, possible sources off a suction leak !

I have the same mower with the same problem. Cleaning the carb make it run great again. Thanks.

Your videos are so helpful, especially for this do it yourself wife who always tries to help my husband out.

Great job!

You have no idea how much I appreciate your posting this. Today - I will put this info to work on my mower. Thanks, sir.

On my John deere x380. Kawasaki COMMERCIAL fs series engine. 600hr on it, has had this exact same issue for a few hundred hours, never dealt with it due to time, but now imma go check the carb! Lol

It's the coil that rides on the fly wheel. And some times need to take sand paper and clean the rust off of the fly wheel

Very helpful video. I had the same problem with my Toro Recycler; whenever I stop to empty the bag, I had to wait until the mover cooled before it would start. I replaced the spark plug, changed the fuel, changed the air filter, but problem remained. I pulled the carburetor and cleaned it and ..... problem fixed. Thanks for posting.

Got the same mower. Hard to start after months dormant. Gotta yank the carb and clean out the old gas. Also, gas cap doesn't like to vent after a few years. I just back it off a few turns to stop the vacuum lock.

Thanks for the video, my Toro shares the same problem. I am guessing that the problem stems from the auto choke. Perhaps the expanding pellet should be replaced occasionally and linkage cleaned?

Exact problem, different lawnmower - Troy-Bilt TB110. Thank you sir! o7

exactly what i needed thank god for people like this

we used to check sheer pin also. Sometimes, man sometimes. Everytime Ive found one jacked, that engine fires up sooo easy after fixing. A couple degrees will kill your arm and lungs.

Gracias por tu video, muy bien diagnosticado. Ahora es mi turno de darle mantenimiento a mi maquina.

Exact problem after getting it back from a full service. Never happened before taking it in. Maybe they fouled the carb? Will try out cleaning tomorrow.

With the ethanol fuel in the mix, when the mower sits through the winter months come spring it's gummy in the carburetor.

I wish I kept my 20 yrs old Toro Super Recycler. My 2 year old Toro Recycler is a PIA.

Did just like the video said. And my lawnmower worked after that.

That one was a surprise for sure. It certainly behaved like a coil going open. You never know!

I have a 2008 McCulloch B&S mower. Used to have a problem every year with the carb gumming up and fine debris in the fuel. Time consuming fixing it. Difficult or impossible to start. My cure was fitting a cheap Chinese fuel filter and stop cock. When I’m finished with the mower for the day I close the cock with the engine running and allow the carb to empty. I use B&S fuel preserver also. No problems for years. It starts right up after a freezing winter here in Scotland. E5 fuel.

great job, my 9 year old Kubota zero turn is having the exact same problem.

I have the same issue with my Recycler. I've cleaned the carburetor, but the problem remains. Like yours, it will start with a shot of starter fluid and continue to run. If I close the choke while it's hot, it will start, though it's stubborn about it. I didn't trying blowing out the fuel line, but it seems to flow fine as it is. I may have missed something in the cleaning, but I cannot think of what. It's a PITA. I have a second Honda mower, but it's a Frankenmower and doesn't do my preferred method of mulching. I also have a Honda riding mower, but it's seen better days and the electrical is an issue, as is several of the tires. My other riding mower, a Ryobi rechargeable electric doesn't want to work either. It drives fine, but the blades won't spin. They do start occasionally, but not enough to be considered even semi-reliable. I just don't have luck with outdoor power equipment.

Simple: Make sure the underside is clean . There are cooling ribs on the bottom of engine. Proper amount of oil. Clean air filter. It will start as it should.

Did you check the gas cap? It is not the spark. Did you fully inspect the carburetor and has it beeb cleaned thoroughly? These are the issues. The gas cap has been known to fail and cause vapor lock On this particular model. I replaced the gas cap with a conventional one which has a vented hole through it. And the vapor lock problems were solved. If you don't replace the original gas cap, then you're going to have this problem again. That's been my experience after owning/operating the same mower and engine for twelve years. Mine starts first time every time. And once a year, one should take all the covers off of the top and clean the entire top of the mower from all debris and grass clippings so that the auto choke works flawlessly. I drain my fuel tank, carburetor and take off the gas cap, replacing it with a tightly fitting rag throughout every winter. Every bit of my fuel that I use contains stabil. The problem I am having with the mower is not the engine. Because I have solved all those problems. It's the body of the mower that is going; stress and fatique cracks around the wheels. The briggs and stratton engines are finnicky, but once you understand the need for a good, fresh fuel And a clean carburetor, they run quite well. I change the oil once a year, along with the spark plug and Air filter every year no matter what. No engine problems whatsoever. You wasted a lot of time figuring out the problem which is rarely electrical.

Today I got a good burn on the carburetor, I was trying to put the wheels higher because it was stopping all the time, I will try cleaning the carburetor.

I had the same problem with my 2006 Troy-built I had to replace the coil works great know.

I just did a cleaning of my dad's trimmer. Same thing, he insisted it was the coil. We took it apart and check the gap. Nothing. So i just took apart the carb, sprayed some cleaner, and put it back together and it works like new. I'm just sad that everything is going battery these days and OEM Parts are getting harder and harder to find.

I have the same issue thanks !

Excellent diagnosis

same problem with mine, thanks for your help

The problem has been like this for years. B&S have done this most of my life.

Wow,ty I'm having the same problem thought it was the coil

Is the automatic choke staying closed when hot? I propped mine open with screwdriver when hot and it started again.

I've got a very similar issue on very similar mower. But I've never taken a carb off/apart before. Any tips? I all ready changed spark plug, air filter and oil. Reckon this must be the issue.

I had the same problem with same model Toro, found the jet was a little gummed up. What are you using as a work stand/ table?

i am going though the same problem with a rental i picked up yesterday

I wish I had watched this before I swapped the Coil on my mower. Oh well, live and learn.

Mine has had the exact same problem. If I wait more than 5 minutes, it's a real pain to get going.....floods out.

I work at a big box retailer..had one returned due to the electric start not working.. replaced the 40 amp fuse (there was an extrain the little black box) and it fired right up..different issue but might be the reason you did not use the electric starter

This is where you always start, clean the the carb and don't use gas with ethanol in it so it doesn't gum up on you.. Usually you don't need to take the carb off just remove the bowl clean it and the jet out good to go.

Hello. Awesome video. I have a Toro 6.75 190cc. I have that issue so I replaced the carburetor and I I took the gas tank out and washed it. Put new gas, new air filter , new spark plug and it starts great but once hot and I turn it off it wont start again. So can it be the coil? and how do I test that?

Do not replace the coil if your mower starts fine when cold. 99.99% of the time, you are wasting your money. If your mower still does not start when hot after you've cleaned the carb and/or replaced the fuel and spark plug, chances are there is really nothing wrong with the mower. You can consider it as defective from the factory. There is a trick to help you start it when it's hot. Slowly pull the rope and stop after you feel it passes the compression release step. Then return the rope and pull it hard. If you cannot get it start after 5 pulls, STOP because the engine is flooded. Remove the spark plug, let it dry, and try again. Hopefully you can get it started in 3 pulls.

Hello I have a brand new Sthil mower and same problem

Plugs almost never go bad. Coils yes, but you ruled that out quickly. People need to run stable in their mowers. This ethanol fuel is crap and will gunk up the carb jet pretty quickly. Did this mower have a primer bulb?

Good job

I will try these steps but wondering how can a new carburettor have problems?

You did a great job

Good explanation

Ive always heard coil. Im having the same issue with the same motor. Ran the carb through the ultra sonic cleaner blew out with air. Now runs great but when i shut it off it wouldnt start. Guess ill clean the carb again.

That my problem with mine also. But I'm not going take the carb apart. I have someone do it that knows what doing. Best to use Non Ethel gasoline

It's the auto choke

I have the same problem even after replacing the plug. I pull the plug, fill the plug with gas, reinstall, and it starts right up. I am sure there is a problem with the carb, but it's a simple workaround.

Same problem, fresh gasoline, use starter fluid, will not start, immediately put new spark plug in and it starts. I have not checked the coil performance. Would like to have seen that procedure.

Great video. What are you spraying into the carburator? What product? Many thanks

Thanks mine is doing the same thing..

I have exactly the same issue and the same problem with starting. Using starting fluid works unless it has warmed up then after 5 minutes nothing until it cools down completely. Replaced plug, carburetor, drained the tank and replaced the air filter. Works well under load and if it chokes off in thick grass it will restart if I do it immediately waiting more than 3-5 minutes nothing until it’s cooled. What is it I haven’t tried a coil maybe…

Weak spark can make the engine cough with fuel ratio contains more air (had the problem recently), it would only cough when I stopped cranking. (Water got on the coil) changed it, it is fixed.

my ryobi mower has been doing this since it was brand new, always seemed like a fuel problem, have to wait ten to fifteen mins before it will start again

I had this problem, but with a new mower only two months old. Can’t be dirt in the carb. I just don’t turn it off when it’s warm, I mulch the grass instead of emptying the bag. If it keeps happening I’ll talk to the seller dealer.

Same problem here.

You habe to press that blue button first couple times Then hold the lever up then start it

I have a similar problem with a Ryobi 2 stroke weed trimmer. I can't restart it after a long run. It has to cool down before it can start again!!!

If the motor runs why are you checking for spark?

You the man!

Does Exactly What It Should Do