Lt 50 quad92
 

Can anyone help I have stripped down the carb to find fault with the running problems. Everything seems fine other than the adjustment screw on the right of the carb the screw doesn't seem to make any difference to the running of the quad at the end of the screw is a what seems like a brass pin which doesn't seem move can anyone help

Welcome to the forums. :)
OEM Parts
Go there and look at the fiche. It shows 2 needle screws. 1 is a air screw the other a throttle stop.
This way you can figure out which needle/screw you have not doing what it should etc.