12hp Briggs and Stratton fires but will not run

I have a 12 hp B&S Mod. 281707-0175-01 Code 8912211(missing a number I think) and it start running slow while my son was cutting grass. I told him to give it some more gas and it ran for about 2 miutes and quit. Could not get it to start back. The next day I was able to get it to start, but not easily and it ran for about 5 minutes and quit again.

I fugured it had to be carb. and rebuilt it, but it still will not run. It will turn over and will run for about 10 seconds (if that much) and quit.

What to check next? I have replaced the plug as well. It almost sounds like it's out of time or something, but it has not been backfiring or anything. And, the couple of times that it did run it would not run with the throttle above mid point.

Any ideas would be greatly appreciated?!?!?!

 

It's the fuel delivery to the carb jets. The tank/filter/line/cap vent - any of those could be plugged.

If you take the float bowl (assuming it has one) off and let the fuel flow past the float valve, it should be in a steady stream. If not, work your way back towards the tank until you find the restriction.

 

how about the exhaust valve seat? I had a 12hp briggs and also a 14.5 ohv throw exhaust seats and they would sometimes start and other times not and would only run but with no power.
Of course make sure it is getting fuel supply first like marbobj suggested.
You can check easily by pulling the head and you would quickly see the problem