John Deere D 110 engine issue

Was working fine then engine slowed and stalled. Difficult to restart and will run at slow rpm even with accelerator lever on full speed. Drained and changed the gas fuel, changed fuel filter, removed and gaped spark plug. Same result. Also when cranking if engine has stopped in compression position the starter motor will not crank the engine. I must hand crank till it reaches neutral position then use the starter to crank. The spark plug appears to be sparking when removed and engine cranked. Wondering now about the fuel pump. The new filter has very little fuel in it - about 1/4 inch of fuel in the bottom. Also perhaps something plugging up the line from the tank. Looking for suggestions what test next. Jim

:welcome:

Please post full mower model humbers and also engine numbers it helps a lot
Otherwise you will get generic information like I am about to give,

Oil , was it full, did you change it if so what did it look feel & smell like ?
Your problem sounds like it is inside the engine
pull off the valve covers and check the valve lash
When the pushrods are not touching the rockers rotate them between your fingers checking for bends.
Both valves should go in and come out the same amount and sit at the same height