[ILLusion]

Your cheapest option in getting this corrected, is just to buy a smaller battery. It may not seem intuitive to some, but the "C" rating does affect the ROF. The lower the C value, the greater the internal resistance in the pack, and thus, the final current output from the pack is restricted. That means, lower ROF.

It's well known that a 7.4v battery will react very much like a 9.6v NiCad battery, so take this in to great consideration when picking the other attributes of the pack, such as max amperage rating, as well as the capacity. The lower the two latter numbers, the slower the battery will be.

The voltage rating is NOT the only characteristic that affects rate of fire. In a "perfect" world, Ohm would be God, and his law would be in the bible with no other characteristics in the mix. Unfortunately, in the real world, there are other factors which contribute to the final result.

This applies to batteries of all chemistries, not just Li-Po.

Try finding a 7.4v 10C or 12C battery with a capacity no higher than 1500mAh if you must absolutely use Li-Po. Otherwise, consider these other options:
1) Installing a voltage control circuit such as the Trigger Master
2) Torquing up the gears to prevent energy build up in the motor (which will also help to reduce overespin.)