Electric Motor

Does the motor have a nameplate?

My 1 HP pool pump is rated at 14.2 AMPS at 120V.

The extension cord is too small/long.

That's all I know.

Another bit of general information (tho' it doesn't have much bearing here) is that the height from the bottom of the pipe to the pump is irrelevant - the important figure is the height from the water surface to the pump.

Good point. My pump only has to lift water about a foot and a half.

Not applicable here, but a centrifugal pump can only LIFT cold water about 15 feet (above the level of the water). The issue is a combination of NPSH and vapor pressure of the water.

At 15 foot lift, the suction is nearly 14 mm mercury- near the boiling point of 62F water.

If the capacitor was no good the motor probably wouldn't start, it could be engaging then failing to disengage, if this is the case it will burn up soon enough as the potential relay is failing....It's pretty hard to troubleshoot something that's not properly installed, with no amp readings or anything really....The motor could just be picking up load and then the empellor cavitating due to air in the line...or it could have some bugs or moisture or surface deterioration on the copper shaft contacts or the brushes might be worn making intermittent contact....there could be a wire broken in the supply voltage making weak contact....The extension cord may only be rated at 8 amps but would still supply 14 amps until it burned up...If you have the time, inclination, tools and skill necessary, I would check the brushes first and amp draw of the motor, make sure I had a good and adequate electric supply....Then if nothing found, take the motor apart and clean the contacts and wiring connections...

Look in the water intake, if the pump has been sitting it may be full of insects/dirt/dust. Some pumps have three or four screws on the intake holding a small grate.

My OOPS, Order Of Probability Sequence:

1. As already said, cord too long / current too high for the cord. 1HP at 120V is going to need at least a 12ga cord if 50ft long. "Cheap" cords are often only 16ga, good for about 10A. So you are causing a voltage drop when starting and so there is a severe loss of torque. As soon as it almost gets to speed, the water starts to flow, which increases the load on the pump and exacerbates the voltage drop, which keeps it from fully accelerating, repeat to destruction.
   
2. Electrolitic Caps on the motor dried out after sitting un-powered for 5 years, worked a few times and then popped.
3. Spider webs / corrosion in the centrifugal start switch (if any) due to neglect. If it was a pool pump it was probably a PSC motor so there wouldn't be a centrifugal switch, but you never know without looking.

By the way, 1HP is WAY over kill for a goldfish pond, unless you want to make fish meal by sucking them in!

Standing around for a long period of time has siezed a bearing with corrosion.

Just a thought!

Stu.

I'd look first at the suction pipe and strainer basket (if equipped) and see it it is clogged or partially clog with debris. Also, you may be experiencing some sort of "air binding" along a portion of the suction pipe, possibly even at the strainer.

The Hayward pool pumps (specifically for the aboveground pools) have a flooded impeller eye because the pool water level is always higher than the impeller eye by a couple of feet. If you don't have that situation you can entrap air in the suction line.

I'd use a sewage submersible pump in your case, one that is capable of passing a 1" sphere.......Hydromatic, Meyers and Goulds are very good ones.

an extention cord is too light to run a 1hp motor.

If its cap start, cap run motor, maybe the run cap is no good, the motor stalls and then goes back to start mode again on the cf switch etc etc??

I'll bet there is a fish stuck in the intake...

"I'll bet there is a fish stuck in the intake..."

As I said, if there isn't yet, there probably will be soon with a 1HP fish pond pump. But most likely unless it was too big for the intake opening, it would be chopped up into food for the remaining fish...