simple they burn themselves up that is why the circuit has a timer :)
The engine won't start or will be hard to start in cold weather unless you have the motor heater plugged in.
no The starter should engage whether the plugs are fouled or not. However, the engine may not start if enough plugs are fouled. If you feel that you have flooded the engine or fouled the plugs you may need to clean them before it will start. If you have caused the carburetor float level or other settings to be significantly changed, the engine will flood and it will not start.
If not gapped right your car might start shaking, or even stall or worse no star.
You may have switched the ignition wires when you changed your plugs. I did this once and my kia started, idled terribly, then stalled after trying to drive. Go back and swap the wires that fit on top of your plugs and see what happens.
nothing happens
No you can't it happens by its self
Glow plugs may not be working properly, or you aren't waiting long enough before attempting to start.
it gets lit
sometimes it just happens... :/
It should try to start at least. It may or may not actually start but you should hear it fire on the 2 good plugs. Why not just replace all 4 spark plugs?
The engine floods and you have to wait for the lawnmower to drain before you start it up again or it might start smoking.
Obviously- the spark plugs were not the issue :)