Briggs & Stratton Lawn Mower Engine Tune Up

  • Thread starter Cameron
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May 10, 2021
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  • #1
In this thread, I'll share two posts that are quite related. They both have to do with fixing lawnmowers (push mowers, to be exact). I'll list both of these posts below. The first post pertains to a general lawn mower tune up and the second pertains to replacing a push mower carburetor. Everything I show you down below is super easy to accomplish, so anyone who enjoys DIY projects should what I share. If you have any questions about any of it, be sure to ask.

It’s that time of year again for my lawn mower tune up…wait, what am I talking about? I have never tuned up my lawn mower, or any lawn mower for that matter. Gee, I wonder why they all seem to run like crap after a few years.

My current lawn mower has a Briggs & Stratton engine. It currently doesn’t run that well. It revs and then loses power, then revs and then loses power. Kind of like … bbbbrrrrmmmm …. nothing …. bbbbrrrrmmmm …. nothing, etc…

I stopped by the local small engine repair shop the other day and talked to the guy. I asked him how much it would be for a tune up. He said, “$70 and under.” I thought this was a little much to tune up a lawn mower that I paid $135 for about 3 years ago. I asked what that included and he told me: spark plug, air filter, sharpening of the blade and an oil change. C’mon, even a cave man could do that. I thought there was some secret stuff they do. I guess not. I told him what was happening and he quickly replied, “You need to rebuild the carburetor.” Hmmm…makes sense, but the carburetor only has a few parts in it (I know because I took it apart on numerous occasions). What the heck could you possibly “rebuild” in the carburetor?

I thought to myself, “If this is going to cost any more than $50, I am just going to get a new lawn mower.” I felt guilty though, because the mower still has shiny paint and it would be a sin to throw it away. Actually, I would just leave it in front of the house and a neighbor would take it as a nice addition to their junk pile in the back yard.

With that guilty feeling, I started taking things apart this morning. I pulled off the carburetor and the gas tank. I separated the two and discovered a small wrinkle in the edge of the carburetor diaphragm.


I pulled the diaphragm loose to see what’s underneath…just a spring. I knew this might be the problem with the poor running performance of this lawn mower, so I started looking through various websites. I found the parts manual for this mower at You have to put your model number (on this mower, found on the front housing) in their Engine Model Number Guide and you can print out a .pdf file.

By the way, you should be thanking me for this…it took a while.

The print out has all the engine parts you might need for this engine. I found the parts I wanted and added the first one to the shopping cart. Not in stock. Ok, on to the next site. I found a nice parts lookup feature at Lawn Cutters Equipment Sales & Service. I entered the part numbers in the lookup feature and they all seem to be in stock. I ordered them and hopefully they will be here within the week.

So, for the exciting part…what did I order? Well, I was just going to order the Carburetor Diaphram (495770) and the Intake Manifold Seal O Ring (270344S). They were about $6 total. Then I got a bright idea. How much for the whole carburetor? Well, as it turns out, the Carburetor (697415) is only $18, so I skipped the other parts and purchased this. It has all that I need included.

I am also ordering the Foam Air Filter Cleaner (698369). With shipping, the order came up to under $30. Not bad. Now I have to pick up a spark plug (Champion RJ19LM) some engine oil and have the blade sharpened. I will put it all back together and let you know how it goes.

I am quite excited.

Past Comments for the Lawnmower Tune-Up Post​

Barry: New product for changing oil.

It is called the LiquiVac Oil Changing System. It vacuums oil out through the dipstick tube. Fast…. in seconds and no oil is spilled, so it is very clean.

It is on sale at Lowe’s in the outdoor power equipment accessories section for only $29.98. A real deal.

Ramesh: I have Craftman 22″ selfpropeller lawn mover, model 917377061, 6.5 hp. I t runs for awhile and llots of smoke and stop. Please advise.

Sam Scott: Iam looking for a good used 18 hp vangaurd side shaft engine to use on a band saw mill i have a like new 10 hp industrial briggs to use as a trade in.

Joe: I own a zero turn john deere 23hp kawasaki engine riding lawn mower. for some reason the engine does not run on both cylinders. this is what i have done to try to fix the problem. 1. changed spark plugs. 2. changed fuel filter. 3. changed air filter.
I have checked to see if both spark plugs fire. (they do).
Finally i unplugged the wire to the working cylinder. I cranked the engine and it took a second or two, but it turned on, i reconnected the other spark plug wire and bam.. it works. I turned it off and crank it up again. Only one side works (the same one as before). I try the procedure once again, and again i get both to fire up. i try to start it up normally and same result as before (only one cylinder is running). LOST, what can the problem be?

Barry (NJ): Hey Cameron,

Just wanted to say thanks. I was taken for the $70 tun-up, I just didn’t want to deal with it at the time. I had my 300zx on blocks in my drive-way with the motor in my garage at the time, and I figured I’d just let the local garage deal with this. Well I got it back, and yeah they changed the oil and the spark plug, and they probably sharpened the blade. But the thing still ran poorly. So I checked, and a carburetor is $40+ so I’ll probably just by the over-haul kit for $7.25 and re-build the carb myself. The Z is back together so I guess I can tackle this next ;~)
I work on my Z because I want it done right, I guess I’ve got to work on my lawn mower now too.

Best, Barry

Chet: well?…. what happened? I have the same problem with my mower and want to know how it went with yours.

Cameron: Well, it ran better than before, but I still wasn’t all that happy with it. It wasn’t that strong of a mower anyway. I went ahead and bought a 6hp Toro.

Jeff: Most of the time surging is a governor problem. Pull the top cover (with the starter mechanism) and you’ll see a plastic “scoop” that the cooling fan blows on. The pivot that this scoop spins on should not bind, often one gets corrosion or debris in the mechanism. Then the governor is always over-compensating, opening then closing the throttle causing the surging. Go ahead and work the plastic paddle by hand to see its effect on the throttle!

F.B.: I have a Briggs-Stratton Wizard on a rotor tiller. Starts and runs ok, but when I tilt the tiller back to move it the engine stops running. It's acting as if it floods out. Can you help?

Jeffrey: My lawn mower was really used when i got it. The speed lever was missing so the RPMs where way to high. I tried to compensate and lower ful intake but it just seized up. i took the cover off as well as the coil-over (aka ignitor) and it started to cycle again. wondering how to get the one i need as well as a new gastank and speed lever!!

Ginny: I have a Craftsman 6.75 HP model #917377180 lawn mower. Initially it would not shut off. Now the spark plug shoots right out when starting it. Pretty sure the plate that holds the spark plug is somewhat stripped….which would allow the plug to shoot out. However, not sure why the lawn mower would not initially shut off. any suggestions are appreciated…thank u, Ginny

Bob: I had the same lawnmower Carburetor pictured above on a Briggs and Stratton engine. I also had the..It revs and then loses power, then revs and then loses power. Kind of like … bbbbrrrrmmmm …. nothing …. bbbbrrrrmmmm. Since the bottom gasket area is made of plastic and can warp easily…I bought a tube of gasket sealer and sealed the bottom gasket and it ran good. Just need sealer on the plastic rail lines on the bottom.

B and S Running Again: i have a 4.5 briggs & stratton engine on a mower i bought 7 years ago for $130. i am a computer repair guy, not a lawn mower mechanic. i looked at several internet posts, decided to try the carb rebuild kit at lowe’s for $2 – $3, plus a $2 spark plug, and voila! the thing started on the 2nd pull! i had almost decided on a replacement mower when i thought “what do i have to lose by trying to take this thing apart?” the instructions for correct placement of the gasket/diaphragm come in the kit, so replacement was easy! i cleaned up everything i could see with my air compressor just for good measure, but this kit actually worked beautifully!

Dan: Thanks brotha.

Alan: I’m having the same problem with one of my Briggs & Stratton engines. Lot of good suggestions here. I’m going to head to Lowe’s to pick up the carb rebuild kit. Thanks for the suggestion.

LowTech Mech: B & S 4.5hp engine on a Bolens branded deck. Purchased 2006. Its been the lousiest, fussiest engine ever. The diaphragm is SOO sensitive. Same predicament as you- low price for mower high price for repairs. For a diaphragm kit purchase online the shipping was going to be 90% of the parts price. That’s dumb so I go to a mower repair shop and buy the kit for $14. Meticulous care of my mower, put it back together and it does not start. I wonder if I got the diaphragm and the gasket on in the wrong order. Thanks to your excellent picture I don’t have to take the bugger back apart again.

I will never again buy a B&S engine again. Honda all the way unless it is a funky commerical Wisconsin Robin engine.

Clue- You know there’s a lot of crappy motors being sold in the big box stores when you see a huge display of starter spray (ether).

Clue- $5.34 cents for a bottle of oil with a B&S label on it. Ridiculous. Engines aren’t that picky just go somewhere and buy 95cent bottle of motor oil.

LowTech Mech: Followup to previous post. I got the engine running. I took the air cleaner off to verify that the primer bulb was shooting a stream into the intake tube and it was not. Mysteriously with my right knee on the ground this time I pushed the bulb and it began to prime. Need a priming bulb for the priming bulb I guess. Its still a good bulb. The engine runs but the plastic link that turns the butterfly valve that the governor arm is attached to has worn out the plastic piece it bumps against. Thus the idle is lower. The engine really needed a idle screw. I will have to build up the seat with a drop of hot glue.

Luwane: My Briggs and Stratton is old .. so old the serial numbers are not in any of the places B&S say they should be … if they were on the cover .. they are long gone … not stamped in anywhere , no plate……… so — I think it is a 10 hp but can’t remember where I got that idea, it’ on a riding mower — it’s a vertical shaft., has points. I want to replace the ignition armature with a solid state one if I can. Where do I start without knowing the engine numbers?

Update: never mind …. I took a chance and ordered an armature that claimed to cover a range of models that I figured this one fell into. It works so never mind. ….. boy I’m good.

Leo: I need help troubleshooting my over 10 years old Briggs/Stratton push mower. It will start but then stops after a few seconds, it will idle at low speed and it will run when the front end is tilted up. I have used carb cleaner and fuel treatment and it ran for about 30 minutes then it quit again. I tried again and it ran for about 5 minutes then quit then back to start and stall. Any suggestions? Thanks.

Joeseph: i have a lincoln electric 5000 gen/ welder need a rebuit/or carb kit . numbers on the unit 25642 type 1135-el 991oo53a. can some one help me i need a cab filter and houseing thanks joe g.

Tony: I think I really messed something up. I had that sputtering problem, then the mower started running real ruff. I began to try to resolve it…by changing …actually just cleaning the air filter. It worked for a while then completely sputtereed out…wouldnt start. Found oil in the carb. Then, here is the “mess up”, I think I stripped the air filter screw. I tried to run the thing for a second without the air filter on…and flooded the carb with gas to clean out the oil. That is when I could not get the air filter screw to screw in. I put a little muscle into it, got a few metal shards on the screw. I think this will cost me a new carburator. Anyone have any advice or experience like this? Would be much appreciated!

Andrew (SF): thanks for sharing your research and listing of all the neccessary parts.
Just ordered all of them today.
btw, the complete carburator price had gone up to ~$30, so i only order the needed parts.
again thanks for sharing.


May 10, 2021
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Replacing a Lawnmower Carburetor​

Remember when I told you about how I was having a problem with my lawnmower? If I remember correctly, I told you that I would let you know how it goes when I received the replacement lawn mower parts.

So, here I am. I received all the parts last week and put the lawnmower back together last evening. Again, this is the list of parts that I ordered, along with part number…

– Lawnmower Carburetor (697415)
– Foam Air Filter Cleaner (698369)
– Spark Plug (Champion RJ19LM)

If you wanted to just order the diaphragm and manifold seal o-ring, here is what you would need…

– Carburetor Diaphrarm (495770)
– Manifold Seal O Ring (270344S)

Of course, this is all for a Briggs & Stratton engine Model Series 10G900. I put the whole thing back together last night and started the mower up. It runs perfectly. I can’t believe that I fixed it. In addition to the new parts, I changed the oil and asked Paul to sharpen the blade, which he did. Here are some photos of the reassembly below…


This is a photo of the top of the carburetor.


This is a photo of the underside of the carburetor. The longer tube sticking out is the primer pump tube and the shorter one is the fuel suction tube.


This is just a picture of the air filter element in the housing.


This is a photo of the extra parts the carburetor kit came with…the diaphragm, the carburetor/gas tank gasket, the fuel screen, the manifold seal o-ring and the diaphragm spring.

carburetor-diaphragm.jpg carburetor-diaphragm-gasket.jpg

I put the spring in its spot and added the gasket as well as the diaphragm just for fit. After this, I actually took them off (except for the spring) and placed them on the proper spot on the gas tank. It is easier to screw the carburetor on that way. I also placed on the fuel screen.


Here is the new carburetor mounted on the old gas tank…


…and this is the gas tank mounted on the lawnmower engine.


This is a photo of the final reassembled lawn mower right after I mowed a little grass. Back together in a snap, but the only problem is…I have two lawnmowers now!

Past Comments for the Replacing a Lawnmower Carburetor Post​

Dickey: dude. i love you! this is exactly what i was looking for to figure out what’s up with my lawn mower not starting!

Adrian: Great description. This worked for me also.

Jamie: Great post with great detail and information! Thanks for sharing! If you’re looking for parts or a great buy on a used or new lawn mower, come see us…

Nancy B: This was fabulous. I’ve been hunting and hunting for pictures of a carburetor. They did not teach us about them in home ec! I found a lot of exploded diagrams, but would have to buy a whole manual to learn that it was right in front of me!

THANKS THANKS THANKS. Your pictures are clear, your writing is clear, and I hope you are having fun with this blog….

Bob: Hi there, just doing a little research on used lawn mowers and found your article among the search results.

Congratulations on repairing your lawn mowers carbouretta. Seems a pretty complex job to tackle when compared to the general mower maintenance side of things.

How long did the job take you from start to finish ?

The bright side of having two lawn mowers though is you have a spare one I guess, plus the satisfaction of having made the repairs

Nice detailed pictures of the carboureta too, thanks for sharing those.

Ken: Fantastic, just what we all need in this lousy economy.
Nobody can afford to pay $70+ to fix a $150 mower every year so you wind up with a garage full of lousy equipment or run a garage sale to clear it all out!

Mike: Great post. Like the photos, and am glad you mentioned the part #’s. Could you please tell us where you ordered them from?

HKA: This is the clearest page showing the carb reinstall, thanks!

Jamie R: Thanks for this post. I just used the information in it to replace my carburetor. So far so good. I ordered my parts from lawnmowerpros.

Aon: Thank you so much for this blog. I was wondering what the bloody thing looked like for starters (carburetor). I found a lot of instructions describing how to change them but no accompanying pics! My lawnmower is exactly like this. I am very grateful. I hope you have a wonderful something and many blessings your way. Sincere Thanks.

Dave: Hehe. And take a chance they won’t fix it either!

Alt: thank you for this very nice write-up and photos… makes my carb clean-up and refit much easier. just one thing… it looks like the shorter tube’s the primer supply and the longer one’s the actual fuel supply… thanks!

Jeff: can you swap out old style carbs for the new primer style non-adjustment units? or is it better to keep the old carbs on them and just keep doing yearly cleanings?

Roger: I appreciate your blog . It was a great help in cleaning my carburetor. I’m still having the problem of not getting fuel though. Can you clean the ball feed tube some way? I didn’t see a way to take it apart. Everything else is clean and free working ,at least the parts that will move.