Chain Guide

This site is a pretty good resource for information about chains and chain identification:
http://www.gizmology.net/sprockets.htm

I still need to measure the go-kart chain to identify it, and research the 4-cycle dirtbike engine sprocket/chain size...
If you find out any info, please don't hesitate to add to the post or leave a comment.

Best guesses right now (online research, no measurements):

Go kart chain: #35
Dirtbike Chain: #420, #428, or #520 -- most likely #520 for engines 150cc and over.

Guesses for the Dirtbike chain have come from the Motorcross section of the Chain Selector at:
http://www.ekchain.com/select.htm

Guesses for the Go Kart chain have come from the TSRacing site chain selection, and from their Understanding Chain tips page.