I have a loncin 110cc quad and I have lots of problems
no 1 spark plug will screw into head but wont tighten fully ,it screws in fully ,and I can tighten as hard as I can with hand but if I use socket theres no tread at end so

no2
Im currently tuning the carb as the engine isn't running good
spark plug electrode is browny ,orange colour??

and when I start up engine a hissing noise is coming out of the intake not where it connects but theres a little tip coming out of intake and theres noting connected to it and that's where the noise is coming from ,its like a spitting noise ,electrical noise ??????

 

{plug the vacuum leak in the intake.causes engine to not run good.}

 

Could the hissing noise be the loose spark plug?

The spark plug hole sounds stripped. You could re thread it OR which is better I think heli-coil it. Heli-coils are just as easy as tapping it and you can go back with the same size thread spark plug.

You are not going to be able to correctly tune or get the performance out of the bike until you get the spark plug deal fixed. That should be first and foremost.

Also everyone should always remember with these bikes that the spark plug threads are steel and the head is aluminum. It doesn't need all that much to seal it off. The aluminum heats up faster than the steel and expands around the steel.

 

How long have you been riding it like this? If you recently bought it have you ever heard it run properly?
I agree with armagh First thing you need to do is repair the threads on the spark plug hole. This is likely the hiss you hear as the engine vents compression or it could be allowing extra air in causing a lean condition. Second you need to plug the vacuum leak on the intake that IS causing a lean condition. There isn't a carb in the world that will have enough adjustment to compensate for these prolems. I just hope you're not already too late! You said plug is a brown/orange color. Black means too rich or oil is leaking int the cylinder, white means too lean, but brown/orange means that the engine was running hot enoug to burn the ceramic. I'm concerned that it you may have a burnt valve or piston/ring to go along with your other prolems. You need to do a compression test when you get the threads fixed. A good rule of thumb for tightening a plug is once it seat 1/8-1/4 turn is plenty.