Push mower keeps stopping

I give up, ignition coil installed and it only want 8 minutes. If it needs a valve adjustment I'll have to take it on somewhere and after that money and all the parts I've put into it I might as well just get a new one. I'll sell this one to someone that knows how to fix it or wants it for parts. So frustrating. Thank you all for your suggestions.
Sometimes, if the repair gets beyond the mowers worth or a repair you can't do yourself....it comes to that.
 
Over Head valve push mower, valve adjustment should be pretty simple, plenty of videos on the interscreen, any good repair man that runs a business will/should know how to adjust valves....
I remember seeing the clearances for the MTD OHV engine.... i think it was .010" Intake and .015" exhaust... that is if my remembory is right ;)
Is it A MTD brand engine or a Briggs and stratton?
 
Hi, I have a MTD 21" self-propelled 139cc OHV push mower. It runs strong for 10 minutes or so then stops. If I wait 15-30 minutes I can usually get the last 10 minutes of mowing done. I have such a small yard and this is really frustrating. I have replaced the spark plug, changed the oil, air filter, fuel filter and fuel line. I've also pulled out the carburetor and it looks clean. I'm imagining that it's overheating but I don't know what else to do to help with that. Any suggestions would be appreciated.
Now you have two good spark plugs.

slomo
 
Sounds like it needs a valve adjustment.
Not from what I've seen in the past. Hard or no starting at all tells me valves. Running for several minutes, then sputtering, is not valves. Out of spec valve clearance should cause issues at all times. 8 minutes then it sputters, she is thirsty.

slomo
 
I give up, ignition coil installed and it only want 8 minutes. If it needs a valve adjustment I'll have to take it on somewhere and after that money and all the parts I've put into it I might as well just get a new one. I'll sell this one to someone that knows how to fix it or wants it for parts. So frustrating. Thank you all for your suggestions.
So after all those parts that are new, clean the carb or buy another one. Did I say that?

slomo
 
Not from what I've seen in the past. Hard or no starting at all tells me valves. Running for several minutes, then sputtering, is not valves. Out of spec valve clearance should cause issues at all times. 8 minutes then it sputters, she is thirsty.

slomo
If the valves are too tight, it will start and run until gets warm, then the valves can no longer seal.
 
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