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I have a Kraftsmann 550 series push lawn mower with Brigg and Stratton engine that runs for about 10 minutes and then sputters and dies. I can start it again after prime it again, but it will run for less than 10 minutes and then dies again. each time I restart it, it will run for shorter time. here is what I have done 1. cleaned the carburetor, cleaned fuel tank 2. replaced diaphragm 3. replaced spark plug 4. replace the blade 5. tried loosing fuel tank cap when it starts to sputter

but non of the above seemed to help.

what else could I still do? thanks for your help

migrated from diy.stackexchange.com Aug 22 '15 at 19:00

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  • 2
    Did you change the air filter? – WarLoki Aug 22 '15 at 18:10
  • yes. I changed air filter as well. – raymond yang Aug 22 '15 at 21:44
  • could it be the ignition coil? but then it would be very weird. why would it work for 10 minutes then stops running. it has to do with engine temperature. when it gets warm, it triggers something to malfunction. – raymond yang Aug 22 '15 at 21:47
  • If it was your ignition coil, it wouldn't start again until the coil had cooled down, which would almost certainly be longer than ten minutes. – TMN Mar 14 '16 at 15:39
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More than likely the problem will be solved with a new carburetor. Ethanol gas can plug ports and/or cause float issues. What you are describing is your fuel bowl filling up when sitting still, then you run it but the feed provides enough fuel to not keep it completely filled (or filled to where it's supposed to be). So after a few minutes of running, it dies due to fuel starvation. You reprime and it starts back up, runs for a little bit and dies again. If you let it sit for a long period of time, the fuel bowl will probably refill and you'd be able to run it again for another 10 minutes or so. I don't know if this is exactly what is going on, but will bet it is fuel related and then the carb is the root of the issue. I've found on small engines, it's easier and cheaper (when you consider the amount of time you spend working on it ... what is your time worth?) to replace the carb rather than trying to rebuild or cleaning it.

  • thanks for your response, when the engine starts to sputter, repriming it does not help, it just dies. so after it shut down, I can prime it, and start the engine again, it runs for 10 minutes again, and sputters and dies. do you think the problem is still with the carb? – raymond yang Aug 23 '15 at 1:30
  • That's absolutely what I think. – Pᴀᴜʟsᴛᴇʀ2 Aug 23 '15 at 1:54
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Just a guess, but it sounds like heat-induced vapor-lock to me. You didn't remove any sheet-metal shielding from between the carb and the motor did you? If so, put it back. And clean any airflow ports anywhere near the carburetor, to ensure that the airflow from the flywheel blows well over and around the carb. I'm guessing you're either missing some heat shielding or you have some gunk blocking the airflow and the carb is overheating.

  • Definitely a possibility. – DucatiKiller Mar 14 '16 at 19:49
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If it's not an unvented fuel cap problem or a carburetor jet problem then it is most likely an electrical problem (coil, points, etc.) that becomes unstable when it warms up to operating temperature.

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10 mins is maybe kind of long for this, but I'd still check for a spark suppressor screen in the exhaust. They can get plugged w/ carbon, and cause similar problems. You can burn it clean with a propane torch. (gently.)

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