Lawnmower starts runs for 3-5 seconds, then shuts down. I had old gas in it and made the mistake of running. Later empties out the gas, and put new in. It ran for about 15 minutes good, now won't run for more than 3-5 sec. What should I do. I replaced oil, spark plug and air filter. Thanks

ive had two of these to fix...its the battery contacts get dirty on the lawnmower battery compartment ive checked wires switchs all fine as other stated,ive cleaned the contacts on the lawnmower side with a fibreglass brush ,and they dont shut down down...anymore rich ,the contacts are shown in picture below ,its worked for me

Need fuel that is not more than a couple months old

Need a good or clean spark plug

Have no idea how old it is, or how many years
you have used it

Sometimes you have to remove the head & clean the
carbon off the piston & head
That is a tune-up on small equipment

Make sure the air filter is clean

They usually start with the air filter off,but you don't
want to do that all the time

Fuel filter?

roght when you leave it for the winter drain the tank ,also on the bottom of the carb is a drain as well so empty it all when stored ,Now what to do now without stripping the carb is to to use the fill pipe to the carb make sure you drain it first and then spray brake and clutch cleaner down the filler pipe so the carb gets filled with this leave overnight and then open the drain plug on the carb and repaet and then try a day or so later ,cant guarantee it will work but it normally works on old VW camper van (carb) and my motorbike .

get rid of dodges

Bad fuel or check for water in your fuel! Clean your carb and float bowl. Empty gas into a clear container, if there is two levels of liquid one of them is water. Of course make sure you have good spark plug.

I would look for the fuel filter. Blow it our. I know you have a new tank of gas, but you might want to empty it out and make sure the clean and put in new. Even with Stabil in the gas you might just have to much condensation in the tank

Oil pressure switch. Check it and make sure oil level is correct. The oil switch will cause this

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I was having the exact same problem with my 6.5 hp Toro lawnmower with a Tecumseh engine. The engine would start up okay but after a few minutes of mowing, the mower would start missing and eventually shut down. I would pull and pull and pull on the starter rope, getting angry and frustrated and eventually going back in the house to let it cool down.

I looked up all kinds of information and I finally decided it was a bad coil (something about the resistance being low when the mower wasn't hot and then when it heated up the coil would conduct enough electricity to somehow make the engine shut down.)

I called a local shop and wanted to get an estimate on replacing the coil. I have no clue about engines so I dared not get into the guts of the mower myself. He told me to check the gas cap. HUH??????

He told me to make sure there wasn't a part missing out of it. I thought, what the heck would a gas cap have to do with the engine shutting down. Well, apparently there is a mechanism on these caps that prevents a vacuum from pulling on the fuel system and my gas cap indeed had a part missing. To verify this, I cut the grass for about 5 minutes. When it started to run rough, I took the gas cap off to allow pressure to escape from the gas tank and voila! it started to purr like a kitten.

So, I'm only out $4 for a new gas cap and I'm as good as new. Man I wish I was more mechanically inclined so I hope your problem is as easy to solve as this one.

Hope this helps!

Could be a defective thermostat in the plenum.
When a gas furnace shuts down the fan(blower) will run until the plenum cools to the safe range. Usually 1 and 1/2 minutes.
Intermittent operation is a defective thermostat or relay.