mower cranks and fire out exhaust and carb. was running when I parked, would not start next day. air filter was dirty and I changed it. New plug. Checked key and it appears solid and in line. Slop in blade engagement, hold it down manually to start. Has compression but feels light. Place finger over spark plug hole does not push out air. Feels like a small tire pump for comparison. Been using premium gas no ethanol. Burnt piston or a safety switch somewhere