lx 178 john deere

i just bought a used john deere lx 178 15 hp kawasaki motor off of some guy it will run for about 15 - 20 minutes then it will quit. i have replaced all the fuel lines new fuel filter checked the fuel pump its working fine checked for vapor look with the gas cap and tank checked both coils one was bad replaced it still does the same thing runs for about 15-20 min any ideas are appreciated the guy i bought it from will not answer the phone so no help there
thanks for your time

"K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts" locate your your engine model manual, download at bottom left of screen & see troubleshooting section.

From memory that model has a low oil cut off so make sure the oil is right up to the full mark ( do not overfill )
It might even have an over temperature cut out as well, Kwakkas & Hondas are a bit over engineered for mowers.

So do a petrol pump test when cold ( crank for 30 seconds into a container and mark the fuel level )
Repeat when the engine is playing up.
They don't necessarily have to be exactly the same just roughly in the same ball park.

Get a nenon tube plug tester
Check the engine cranking cold & idling cold
Repeat when engine is playing up.
Best done some where reasonably dark

Locate the magneto cut out wire.
When the engine is playing up undo the wire
NOTE YOU CAN NOT STOP THE ENGINE TILL THIS WIRE IS RECONNECTED ALL SAFETY CUT OUTS WILL NO LONGER WORK POTENTIAL DANGER.
Problem goes away then you are looking at a fault in the safety switches.
Make sure you dissengage the blade & they have stopped before you get off the mower as it is real easy to slip an ex-toe under the deck while reconnecting the cut out wires.