pedro,
First remove the throttle by unscrewing the top ring of the carby and at the top of the throttle is a small screw, turning this in a clockwise direction (which lowers the needle)will give a weaker/leaner mixture.
When adjusting only turn half a turn at a time till you get it to the correct setting.
I am working on uploading the manual and hope to have it done by the end of the week so that you will be able to download it.
