how do we decide which motor(RPM of motor, voltage etc)is suitable for a given CC BIKE ??PLZ REPLY SOON

Hi Sunil, to make an engine start it must be turned at some speed, so that it sucks fuel and air into the cylinders, and compresses it. The powerful electric starter motor does the turning. Its shaft carries a small pinion (gear wheel) which engages with a large gear ring around the rim of the engine flywheel.

The question you asked need to do precise calculation based on physics, for instance you need to know how much force is required to turn the motor of that engine, and then on the basis of that calculation, you can device electric motor which produces similar or equal force. I am not physics nerd, could have helped you out.

You may see following links, go through them, may be they can help you out..

HowStuffWorks "How Automobile Ignition Systems Work"

How the starting system works | How a Car Works