Two service manuals for Chinese scooters with GY6 engines can be downloaded below, along with 1 troubleshooting guide:
Arrow 150 (2.5 megs):
http://www.hondaspree.net/other/arrow15 ... manual.pdf
General GY6 manual (20 megs):
http://www.hondaspree.net/other/GY6_Ser ... Manual.pdf
Tank GY6 troubleshooting guide (0.5 megs)
http://www.hondaspree.net/other/TankGY6 ... tGuide.pdf
These two manuals show up in several forms for a variety of different types of vehicles, including 4-wheel carts and buggies, and concentrate on these widely-used powerplants. Chances are, if you have a Chinese bike that's 4-stroke, it's a GY6 design.
Troubleshooting guide is generic to all GY6 bikes (as well as most others.)
For body and general repair (which is not covered in these general manuals,) the Honda General Service Manual is an excellent resource on general motorcycle repair techniques. It is available here in the Honda manuals section.
For upgrades to these engines, I've found the following posted elsewhere. Use at your own risk.
Upgrades for GY6 engines (300 Kb)
http://www.hondaspree.net/other/Mod_Kit ... ooters.pdf
Chinese GY6 service manuals and troubleshooting guide
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Chinese GY6 service manuals and troubleshooting guide
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