Be careful when running transformers at voltages that are considerably
higher than the design values.  The insulation in transformers is
generally quite robust, but it has its limitations.

Most transformers are not really as symmetrical as you'd expect, and
there is also a possibility of saturating the core if currents are too
high.  This cuts down the output voltage drastically and can distort
the output waveform, which induction motors won't appreciate.

I have two suggestions.  First off, check the motor and make very sure
that it is not a dual-voltage device.  A great many 240-volt ac motors
(and power transformers, as well) can be wired to run at 120VAC.  The
windings are split and the two parts are connected in series for use
with 240v and in parallel for use at 120v.

If this won't work, step-up transformers are available through
wholesale electronics suppliers.  You must, however, know the power
requirements of your motor.  These transformers can be expensive,
and the prices may also vary wildly depending on the supplier.  Two
isolation transformers (120v/120v) can also be used to step up the
voltage, and these may cost less than a single step-up transformer.
Electronically-based 120/240v converters may also be available --
I haven't checked in quite a few years.

Let us know how this all works out.

Mark Kinsler
Lancaster, Ohio USA
http://home.earthlink.net/~mkinsler1/