4 cell? Depending on your track size i would start with a rollout around the 41mm range.. if need be go higher and start gearing for run time. Its better to be a little bit slower and make run time, than go full blaze and crawl home.. Which you cant do with lipo or you will drop it below the optimal voltage and damage the pack.

If this dosent work the battery may be damaged. But i would suggest muckng around with gearing first.

Antoni