Right here's how to properly flush out an old or dirty motor:
1. Remove from chassis.
2. Get a glass jaer and fill it up with either lighter fluid, white spirit, or a similar kind of cleaner.
3. Very Important! Emerse motor fully in liquid. FULLY. make sure everything except the wire are under the liquid.
4. Hook up to 9 volt battery. Not power supply.
5. Shield anything important; eyes, mouth, carpet.
Reasons: Fully emerse the motor because, as someone said earlier, the arcing can sometimes ignite the liquid. Not so, when it is fully emersed.
Don't use a power supply, because sometimes the liquid conducts and sghorts the power supply. At the very least, you will need a new power supply, at most an electrition to rewire your house...
Shield everything. Sometimes the liquid will splash a bit. As it's a powerful cleaner with loads of motor carp in it, itr could blind you or worse, wreck you mum's or your spouses carpet. Either place the jam jar lid back on or just do it on a tray.
This is how I do it, but I am in no way responsible how any injury resulting from ignition, blindness or a clout round the ear. After doing this, give it a bit of a clean with some water, then run it till it drys out.
When you just want to"juice" motor, while it's still in the chassis, get chosen liquid in a syringe or squity bottle. Spray on to Com and or brushes, and lightly on the bearings at each end of the shaft.
Useable liquids for squirting are: lighter fluid, switch cleaner, wd40, duck oil, white spirit, RC Com drops or other cleaning fluids.
After squirting, run the motor with a 9v battery for a couple of seconds.
Motor speed can increase by up to 50%. Just try it. Make sure that it's all dry before you put it on the track, 'cos otherwise you'll be disqualified, or screw up the track.
Hope this all helps, anything else?