didi you find out what is the problem was ?
I have the same problem with a GY6 scooter : the pressure is good : when it touches the ground it shuts off .. the piston and rings are new , the cylinder gasket is manualy made in cars gaskets maker workshop it is made of klingrit 1.2mm thickness mixed with metal , because I could not find the original cylinder head gasket which has two rubber paint on it and not totaly metalic ... what happens is that : it works for one month very good , but the valves cover vent is pushing oil out to the tube which is going to the air filter ... then after one month it started to get black smoke and shuts off when the rear wheel touches the ground or press brake lever and make black smoke from the muffler , I do not know how the oil goes to there to the piston ??? no problem with the pressure and it works at idle on stand, as why the valve cover vent brings oil out ??? I have seen many people are suffering of the same problem but no one could tell where is the problem ??
1-when i go to adjust timing chain big hole and two small holes on the sides : ( I noted that the drive chain is a little streetched so one of the side holes is a little advanced of the other side hole , there is no way to adjust better than it : so I had to accept this result .
who can help ??? everything is new and professionaly installed as I am a mechanic but this problem is new for me ..