Lawn Mower Won’t Stay Running? Briggs & Stratton Carburetor #799866

This video provides step-by-step instructions for replacing the carburetor on Briggs and Stratton small engines, commonly found in lawn mowers, riding tractors, zero-turn radius mowers, wheeled edgers, pressure washers, and generators. The most common reason for replacing the carburetor is if the engine is hard to start, leaks gas, runs poorly, won’t start or stay running.

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Additional small engine repair, troubleshooting tips, help with finding your model number, and part replacement videos:

All the information in this carburetor replacement video is applicable to the following brands: Briggs & Stratton

Tools used: flat-head screwdriver, Phillips screwdriver, nutdriver, clamp cutter, socket wrench

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43 thoughts on “Lawn Mower Won’t Stay Running? Briggs & Stratton Carburetor #799866

  1. I replaced my carburetor but the choke lever assembly was not able to move at all when I put it back together. Did I miss something or did something come detached under the motor housing that would me it tight? 

  2. How much play should be in the choke lever assembly while carburetor is off…….I have mine off waiting on new one to come in but I feel worried about that choke lever assembly it is really loose… that a problem or is that normal?

  3. hi,
    Would apprec some help and advice. Used you video and all seemed well. Mower worked for one long cut with multiple starts. Week later started for couple of second and I turned it off to adjust height setting and now it will not start no mater what (fuel and oil levels ok). Have checked and spark plug OK (using multimetre) and there is current from the magneto (used tester that lights up). Motor does not even seem to turn over. Just pull cord and magnet etc works but no ignition. Tried with out filter, tried to spray some carb cleaner into carb in case it is not priming (has auto choke and primer). Fuel is held in can so no chance of water in fuel etc. Auto choke arm sitting OK and moving correctly. I am now stuck. Any ideas.

  4. I have a brand new Stow & Mow and the engine doesn't seem to be running well. It takes a while to get up to full running speed and dies quickly when going through thick grass. I have to lift up the back of it from the handle and it gets running quickly again, but doesn't last long. It also smells likes its running rich. Strong fuel smell. Cleaned the air filter and carb… both looked fine. What could be my problem?

  5. Just got a question. Is there any other reason for the engine to start and stall out besides the carburetor? Or should I just go and get a new carb.

  6. Hey , I accidentally mixed the wrong fluids into the wrong tank. Now my mower wouldn't start after I drained the fluids out of the fuel tank and replaced it with ethanol free fuel. Do you have any Idea of what might be the problem?

  7. Thanks for the clear instructions. Most of us in New Zealand want to just clean out the dirt that is blocking our jets in the carb, rather than replace the whole thing, must be our pioneer roots… Are you able to give some instructions for this please? I am having problems with a similar (older but similar model 129802) Quantum engine that starts and runs at good revs for a few seconds but cuts out suddenly as if the fuel flow (or spark) has stopped. I've dismantled and cleaned the carb, and noticed what looks like a welsh plug in it, (possibly covering up a couple of fine jets?) I've checked the tank is venting OK as well. There are 2 holes in the centre of the carb above the bottom nut / jet, one of these goes to the brass tube in the venturii air flow, where does the other one go? Thanks for any help.

  8. What about the primer bulb and assembly. Is there any reason to look there and perform some kind of maintenance before changing out the carburetor?

  9. Worked perfectly! Thank you so much! Even when brand new, this mower gave me fits trying to keep it started and I chalked it up to bad gas. I think it came fully loaded with a bad carburetor!

  10. i do small engine repair, their is no reason to buy a new carb. 90% of small engine problems is a fuel issue, clean the jet ports out and it will run! AND dont leave it in the rain, the gas cap has vents in it, water will get in your fuel

  11. Really stuck here. Had the exact same issue as everyone else…would start from primer and then stop. Totally removed carb. Cleaned with carb cleaner and pipe cleaners to clean all ports and tubes. made sure too get holes in bowl plug. Changed out gas, and used rebuild kit and replaced gaskets and needle. mower started and ran great last night. when it got dark put it away and now doing exactly same thing today when tried to finish yard. Took back apart looking for any clogs or dirt, nothing… any ideas on what could still be the problem?

  12. title is incredibly misleading. Just change the title and it's a good video. just wasted 3 minutes of my life

  13. I understood the title perfectly! Since I have a front, back and side yard to mow, I have been using the engineered , 4 cycle gas from Walmart or Home Depot, more expensive for sure, but my mower does start every time and even after harsh, upper midwest winters. Thanks for the video!

  14. I like this video. It showed me how to repair a lawn mower (Briggs and Stratton) that start and die. It's very helpfull . Many thanks.

  15. I replaced carb and started mower it ran rough and eventually died. I figured the choke wasn't opening up as it was spewing black smoke. When I pulled it apart I found that I had managed to jam the air vane/choke lever so that it wouldn't operate. I removed the screw holding the air vane /choke lever in place and managed to set it up so the choke operated freely. I put it back together and now it won't start at all. Any ideas?

  16. use premium fuel in small engine , for some reason it works better and does not gum up in a carburetor after long storage ,
    second if you have a fuel valve turn it off while the engine is running and wait until the fuel dries out from the carburetor ,
    Fuel left in the carburetor for a long time will dry up and damage the carburetor , installing a fuel shut off valve is easy ,
    If engine is hard to start remove the spark plug and use a propane torch burn off the Corbin residue and whatever might be on the spark plug , I do it until the Central Electric and the ground electroid get red hot , of course wait until the spark plug cool down before reinstalling it , in the Old Country Palestine we used to put a small amount of gasoline on the ground put the spark plug in the middle of it and set it on fire , that always worked to get us out of a jam ,

  17. This video explains absolutely nothing on WHY it wouldn't stay running. Sure replacing the carb, is one way, but, why not explain why it wouldn't run ;then go from there.

  18. since we're just replacing things rather than fixing them, why not save all the troubles and just buy a new mower?? better still send someone else out to buy it for you and have them mow the lawn…

  19. I could save I money on the carb… that little nut on the bottom of the carb isn't just a nut it's a fuel jet clean that mofo out and install it back ur lawn mower is running again

  20. There was no need to replace the carb. just clean it and it should be fine unless you want to rebuild it. The gasket was ok, no need to replace that either. This is all wrong, do a little work for a change and stop screwing the customers for new parts when they don't need them.

  21. A video by someone who sells carburetors.  The real problem 90% of the time is a clogged fuel jet which is in the half-inch nut on the bottom of the fuel bowl (or just water in the bowl itself, both of which can be easily fixed by removing nothing but that nut and fuel bowl assembly, which can be reached from the front without removing anything else.  Sad part is that the entire issue could've been prevented by the use of an in-line fuel filter which they didn't build in.

  22. So i changed my spark plug, carb, and air filter, all brand new.. it fixed the putting and smoke but now it only runs for maybe 5 min then dies and wont start up at all? What do i doooo?

  23. Men i need your advice! just bought a new mower brand new my lazy son didn't want to cut the yard. Now im out here trying too start my mower but it want start! White smoke bursted out and it shuts off..Any suggestions? please help before i hurt my 14 yr old son lol

  24. it is cheaper now a days with time and parts, to just replace parts though, deal with that alot in the marine industry, we used to disassemble and clean switches and solenoids and other electrical parts, now they get replaced, for dependability and longevity, also parts arent made here, theyre made overseas… CHEAP, so they can be replaced cheaper than repairing

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