I have a Sears self propelled 22" deck push style mower that’s about 7-8 years old. Once primed it runs for approx 2-3 seconds then stops completely. I cleaned the plug, filter and checked the fuel hose. Fuel ran readily from the tank when it was disconnected and the hose line is clear.
The filter an plug were dirty and needed to be cleaned, but this did nothing for the problem. It’s as if the mower is burning the few sprays of gas I’m putting into it from pushing the priming bulb and then no more gas is being delivered or burned.
Have you checked the throttle cable? Sometimes this breaks or becomes disconnected from the carburetor, which keeps the engine at a low idle, and I know some of the mowers I’ve had would not run at idle until they’d warmed up for a bit.
Failing that, and since the mower is 7 or 8 years old, have you had it in for a tune up any time recently? The carburetor itself may need to be serviced: new gaskets, other minor parts…any small engine repair shop can do this for a nominal sum, thirty or forty bucks in my experience.
If your machine hasn’t been serviced in a long time, it’s not a bad idea to bring it in for a tune up anyway.
Has the mower been stored for a while with fuel in it? If so its a good bet that the tank pickup tube/fuel line and or carb jets are clogged with varnish left when the gas evaporated over time. Taking the fuel system apart and spraying the hell out of everything with “Gumout” carburetor cleaner will cure the problem most of the time. I have used this trick to get several motorcycles,lawnmowers and automobiles running again after they had been stored with fuel in them.
I’m going for a dirty needle/seat in the carburetor. I’d bet that as the float drops due to the gas in the carburetor bowl being burned, the needle is not dislodging from the seat, so no gas flows in. The priming bulb forces it in under pressure, forcing it past the dirty needle/seat, but gravity alone isn’t enough to open it.
That’s been my experience with this symptom anyway. Take off the bowl, take out the needle, and give it all a good blast with carb cleaner. Put back together, and you’ll likely be in good shape.
I have a lawnmower that I thought was suffering from some type of fuel clog. I inherited it from the person I bought my house from, I suspect it was never maintained in any way so, like yourself, I started by changed its plug and filter and it would still stall. I used multiple gentle squeezes of the prime bulb to keep it from stalling once it was running and after a couple of minutes of this the lawnmower started to idle normally on its own. It ran like a top all summer. If that fails, go with the cleaner / rebuild.
The fuel pickup could be glazed over from old fuel. If you’re cleaning the carb out then make sure you check the pickup. don’t just look at it, make sure it flows freely.