[GZ250]

Again the thing is to clean and get rid of the old junk and oil residue and then you will be able to figure out where the leak is. use kerosene oil and a brush to wash everything away. if you pull this black wire up, you will see a single spark plug. Clean this nook with the spark plug, head and fins, valve covers and all the area around. if you remove the tank you will see everything easily. After cleaning with oil you can wash with water or without that start the bike. It will burn the oil away and then you can go for the leak.


PS: it seems that you are very new to the machines or bike, so first get get used to the names and parts and then do anything. I would suggest do not try tightening even with a torque wrench at this stage. First clean the area and see if you can figure out yourself or get some help from a friend or a shop. It is very easy to ruin something. Careful learning is another thing.