i'd use 25h instead of regular 25 chain. its pretty much exclusively sold by scooter and gokart venders.
http://www.partsforscooters.com/25H_roller_chain
http://www.amazon.com/Mini-Pocket-Bi...dp/B0059ZPHEU/
25h is rated at 1750lbs while regular 25 is rated at 875lbs. 35 is rated at 2100lbs.