The Sidedness of IC2C is different, try inserting an Automation Upgrade using the Tool that looks a bit like but with a wrench below it.
You can just hopper the Fuel from the top or side instead (that way the Generator is vanilla compatible).
The Bottom is for Charging stuff in IC2C.
I somehow can't believe that you didn't even try other Sides before reporting it. Especially since the Tekkit Wiki applies to IC2 Exp.