Most everybody is members on both forums.
1. I'm gonna say its a short. The ground system on these are soldered and known to be problems. Something else is to look at the rubber on the intake. Chinese rubber is subpar at best and they are known to crack.
2. You can't put too big of a battery or it will overload the charging system. I run a lawnmower battery on mine. You can pick them up for around $20. It is bigger than the tiny one that it came for and I built a new battery box for it.
3. it's the sprocket on the rear axle. You can look at it and see everything you have to remove to get the old one off. I'd suggest oiling everything down well before you plan on trying to slide everything off the axle. Things like to rust weld back there.
4. Without a flow bench you can't tell if you are doing any good or making them flow worse. Just hogging the ports out bigger does not always mean its better. I'd suggest just cleaning up the rough casting in the ports and making the ports match the gasket. Grind out what you have to and blend it in about 1 inch down the port. On the intake track you want the surface finish a bit rough but the exhaust is where polishing it is good.
5. I use 75w90 synthetic, brand choice and normal/synthetic is personal preference.
2nd post in this thread has pics and pretty much nails gear oil change on a gy6
http://49ccscoot.proboards.com/threa...gearbox-change
I think I told ya over there when I got my buggy it was pretty much in the same shape as yours. I ended up ordering all new electrical stuff (cdi, starter relay, etc) and pulling the entire harness out and going over it with a fine tooth comb. I resoldered all the joints and added new heat shrink to them. I also replaced the plastic connectors because mine were brittle and breaking if you looked at them. You can find the connectors cheap on ebay but they ship on the slow boat from china. I was lucky my brakes worked fine but I did replace the pads. Right now I'm replacing all the bearings and bushings. The bearings I'm changing them out with quality ones. The bushings I'm using urethane, most of which I'm having to custom make.
Got mine cheap as a runner but has turned into a frame off resto. Wouldn't have been so bad if I knew it going in but what I get for sending my brother to check it out.