When it comes to deciding what to use, you need to know the basic rules. They are that an A2 bike can’t have more than 35kW – that’s 47bhp – and it can’t have a power-to-weight ratio of more than 0.2kW-per-kg. So forget those ideas of a featherweight GP3-bike-for-the-road – if a bike makes the full 35kW, it needs to weigh at least 175kg.
However, restricted bikes are allowed provided they didn’t make more than twice the 35kW limit in their original form. That means stuff with 95bhp or more as standard is ineligible for restriction, however little power you eventually intend to restrict them too.
Some countries have restrictions for beginners, if you're not from Europe or Australia you don't need to worry. In North America they have the wonderful practice of letting the new kids on the liter bikes right off the bat.Some companies release mods so that their bikes can fit into the restrictions that some countries have. This is the restriction on your license right?