DC motor control ULN2803
@WesleyLee got me on the right track; it looks like the starting voltage has to be high enough to get the motor spinning (at least initially).  

The sketch below will get the motor running at a very low voltage:

void setup() {
  Serial.begin(9600);
  pinMode(14, OUTPUT);
}

void loop() {

  analogWrite(14, 1023);
  delay(15);
  analogWrite(14, 200);
  delay(3000);
}


It's not a beautiful solution but I suppose it works for my application.  That's what you get for buying cheap pumps I guess.