A collection of links to pages I've found useful.
About GY6 Tuninghttp://www.rc-trucks.org/gy6-engine-performance: Made for gokarts, but just as useful anyhow.
My best source for spare parts.Mopedfactory [Kevin Huang] on Ebay. Usually has low prices compared to other sellers.
The GY6 engine even has it's own Facebook group.GY6 Facebook Group. Some of the guys in there are pretty skilled.