Brand new motor cycles on/off every second.

I'm stumped. I have a 1hp Hayward super pump. I'm not sure how old as I just bought the house 2 years ago. When I opened the pool and went to start up the pump the motor hummed. I disassembled the pump and checked the motor with nothing connected and it stilled hummed. So I bought new motor and new seals. Installed the new motor and seals. The pump ran ok for a few minutes and then it would cycle on and off every 1 second. Disassembled the pump and motor to check everything. Everything looked fine but I ran the motor with nothing connected and it ran fine. So I reconnected it and the Same cycling problem happened again. So I disconnected the piping to check it again but first I ran the pump with no water for 15 seconds and it ran fine. The motor only cycles when the water is flowing through the pump. So I figured the motor was bad and had a replacement sent.

Reinstalled the new motor and I thought everything was ok. It ran for a hour as I vacuumed the pool bottom to waste on the sand filter. But when I shut the pump off to put it to sand filter to filter and started it back up, the pump motor started cycling again. I could get it to run for 30 minutes or so if I had both the skimmer suction valve and main drain suction valves 1/2 closed and the pump would run but it would eventually run hot and motor thermal overload would shut off.

So I'm about ready to just give up and buy a whole new pump and motor unless anyone has any suggestions.

Would you please give us model number nameplate information of the new motor and old motor (HP, SF, Watts, Amps, etc.) as well as model of the pump (wet end)?
I'm guessing that the replacement motor may have a lower Service Factor than the original. Cheaper than a new pump, you might be able to downgrade the impeller.
What's the voltage at the motor? If you have a long run or low voltage at your service, the motor will draw more Amps and overheat.

I threw the old motor away before the new motor arrived as I figured there was no need to keep it and it die on trash day. So I can't check it. The pump model is Hayward sp2607x10. Per the Hayward brochure I just found online the pump/motor has the following info. 1 hp, 1.1sf, 230/115v. The previous motor appeared to have been the original motor that came with the pump.

The nameplate on the new motor is 1 hp, 230/115 and 1.1sf. So it matches. Below Is the amazon link where I purchased it.
http://www.amazon.com/Electric-UST11...ywords=Ust1102

The voltage at the motor is 230 but I have not verified it with a multimeter yet. And it's a replacement so and the old one worked fine for the past two years I've own the house. I may check the impeller to make sure the previous owner did not put the work impeller in for some reason. And the breaker at the main panel was 230 so I'm pretty confident that the problem is not with the power to the pump.

Sounds like the motor's the same (it's not the UCT1102 is it?). Check the wiring, check the voltage, check other wiring connections that may have been disturbed. A bad connection can be the cause of high resistance which would drop voltage at the motor.

One possibility: the pump is wired incorrectly -- there are many ways to do so. Another is: the pump is set to 120V but supplied with 240V.