There could be a short in the timer. Do you have the timer wired correctly that maybe when the contact closes, you are putting the hot directly to the ground? It could be that the way the timer closes the contact, it causes a greater inrush current that just by the pump itself and thus trips the breaker.

There's a miss wiring at the timer ,which may neutral it's connected to the hot pole and it make short when timer it go on.

All timers have a max hp or max power rating.

They will drop Voltage and brown out motors if overloaded,

Your timer must be rated for a motor (inductive)

load greater than the motor's requirement.

Probably stalls due to not being off long enough to drain the back pressure.

are you sure the breaker doesn't need replaced?

submersible 110 pump with 2 wires and a ground-- plugged directly into a 20 amp circuit works. When I plug it into a timer (tried 2 of them), and then into the circuit, it trips the breaker when it should turn on.