Just picked up an old Murray 20 push mower with Briggs & Stratton 3.5 Classic engine. When cold, it starts up fine and seems to run strong. After about 5 minutes of mowing, power seems to drop, doesn't run as smoothly and then dies and won't restart until it rests for quite a while and then cycle repeats. Would appreciate any advice on troubleshooting.
Also typical of a punctured diaphragm on the fuel pump,
partially blocked fuel filter
hole in the fuel reseviour inside the tank.
Valve lash that is too small will also do some thing similar.
As the valves get hot & expand they touch on the pushrods & don't quite close fully
I opened the fuel filler cap and was surprised to see that the mower ran through almost an entire tank of gas after running only 15 minutes or so. The gas consumption is abnormally high. Could there be an issue causing fuel flow to be way too high and also possibly causing flooding that might explain what I'm seeing?
I would check the valve lash first. The intake may not have enough clearance and when it expands from the heat of running it no longer closes fully and you get combustion gases forced into the intake.
If they are in spec then I would next check the ignition coil. Good luck.
