How do you make your 125 XTZ Yamaha faster?

The XTZ 125 and TTR 125 share the same engine. So actually there is a lot you can do. 1: remove the snorkel under the seat that goes to the airbox 2: remove the screen in the air box(these will help increase airflow). Or if you want you can completely cut out the top of the airbox or put a uni pod filter on the intake, but you will have to re-jet the carbs for those two.

Besides that you can get the 'TTR 125 Big Bore Kit' by BBR which you can safely turn it into a 150.

Carb from a 200x atc also works wonders.

its not going to happen i have tried