The data sheet says your MOSFET has a gate threshold voltage in the range 2V-4V
i saw that too, so even the lower 4.93v is still more then enough, but the 3.3v on the arduino board does not work, only the 5v. i dont get it.
What is the voltage between the MOSFET gate and ground terminals?
im at work now, ill test that tonight when i get home.
Are you certain that the only change between the working and non-working circuit is that you moved the wire from 5V to pin 9?
i was just unplugging the wire that goes to gate from pin 9 and moving it to 5v, it would start and stop as i did that.