Engine Cub LT1018; 18.5 HP B & S motor

[StuckinOhio]

Motor will only run with choke fully "on". When I push it in to turn off choke, motor "misses" then shuts off. Anybody come across this?
Any ideas on fix?

 

[BlazNT]

Dirt in gas, carb, fuel lines, or fuel tank. Time for some good old fashion cleaning.