Weirdness from my lawn mower

Year old walk behind self-propelled. Sometimes it won't start, other times it starts and runs for about 10-15 minutes and stops. Even if starts, when I turn it off to get drink of water or other reason, it won't start again for an hour or two. It just doesn't catch when it won't start at all. No sputtering, etc. However, when it does start, when it stops on its own, there is usually a faltering and then it stops. Almost like a vapor lock. Any ideas of what is happening and how I can fix it? It is new gas (actually less than a week) and the can I am getting it from was bought new for this season so I doubt problems with that. I cleaned the foam air cleaner after every use because parts of my lawn are fairly dusty.
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On Monday, May 28, 2012 7:55:38 PM UTC-5, Kurt Ullman wrote:

My guess is a heat-related magneto.
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I was thinking either an ignition coil / magneto that is affected by heat. Or, inadequate valve clearance. I've also heard that cheap grade of motor oil can cause similar problems.
Christopher A. Young Learn more about Jesus www.lds.org .
My guess is a heat-related magneto.
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A few times I had that issue it was electrical as in ignition module or coil , start with a new plug and check plug wire, to me the fact when you turn it off it won't start again shows it could be the module as it gets hotter after its shut off, that would be a time to remove the plug , ground it and have someone pull the mower to see if you get a good spark. Or spray gas into the carb to see if it's fuel related
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wrote:

Drain the carb.
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Kurt Ullman wrote:

If the tank and carb were not run completely dry before winter then it is likely fuel related. Try some Sea Foam in your fuel.
It isn't all that unusual for a gas engine to not fire after being recently shut off unless it is left to idle down for a couple minutes (due to fuel in the cylinder). My RX8 must be warmed to operating temperature before being shut off or it's a tow to the dealer.
It isn't very likely at all that you'd have any sort of electrical failure on a mower that new.
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It worked fine the first 6 weeks of the season. WHy start now?

I don't think I have anything electrical on the mower anyway.
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The ignition coil, spark wire, and spark plug, and magneto. Are all electrical parts.
Christopher A. Young Learn more about Jesus www.lds.org .

I don't think I have anything electrical on the mower anyway.
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Kurt Ullman wrote:

The inferior gas/ethanol tends to build up a yellow gunk inside carbs if not thoroughly emptied over the winter season. All it takes is a small piece to break loose and give problems. Sea Foam does a very good job of cleaning carbs. This is a simple procedure you can do yourself and very cheaply.

SM has already corrected you on that issue.
If it's electrical it's going to probably be a trip to the shop as it isn't likely from your posting that you'll be doing that yourself.
Other than an engine being simply worn out (or oil neglected), nearly all problems come down to fuel or spark. And from many years of mower experience --> it's a fuel problem 90% of the time.
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Since we can only guess, I would do the following.............
Check to make sure the vent is working onthe gas cap. Change spark plug. Make sure the "dead-mans" switch is working correctly and not sticking (cables CAN stretch). Like one poster suggested, when it won't run, try spraying a little gas in the carb ot see if it is fuel related and check for spark. You can't fix it if it isn't broken. :-)
If all this checks out ok, I am guessing a sticky valve or leaking head gasket.
Hank <~~~~ professional guesser
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I've bought bad plugs at stores and several times have seen them sitting on the floor where customers dropped them
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On Tuesday, May 29, 2012 5:30:16 PM UTC-5, ransley wrote:

Bad plugs! (maybe you should use that as your sig?!)
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