Ah, the (dis)advantages of the low-starting-voltage and high-torque coreless motor! 
Funny you mention this. Many of the engines I've built or repowered with coreless motors have had
an annoying (

) habit of "walking" along when a DC throttle is turned all the way down to "zero".
Many DC throttles will leak a little voltage on the outputs unless there is a small load on them,
and apparently 10-15 mA is not enough to pull them down. Add to that the fact that a lot of coreless motors
will start turning with usable power at about 0.7 volts, and there you go. The engine will just creep along.
I have long since gotten around this by tweaking my home-made throttle so it doesn't leak, and rigging the
speed control pot so that no pulses at all appear on the output when the throttle is turned all the way down.