The old Primer debate. It seems to be happening more in recent times. Maybe checks are declining.
If not locked in the primer will allow the engine to run like a Fergy tractor and will make the pilot think that an engine failure is about to happen.
When this subject comes up it always reminds me of the over-confident instructor at the flight school I was working with at the time. Said instructor ways knew more about everything than anyone else and was quick to let everyone know that he knew more than them.
One day said instructor brought a Warrior back from the run-up bay and complained to the engineers that the engine was running extremely rough and that he felt it had a major problem. An engineer checked out the aircraft and returned it to service after he had written up the paperwork as follows; 'Aircraft reported to have a rough running engine. Fuel primer
found unlocked. Primer locked in position. Engine operated normally. Aircraft returned to service'.
For ever afterwards the engineers always had a sly smile when said instructor was around. I know why.