not very much really might rev a bit harder with no load on the back wheel but other than that its a waste of money.
there to make use of high revving cylinder/exhaust combinations... fuck all use on a stock bike. as is anything. not gonna get speed for free/verry little money, the engines are just too shit to start with need a decent kit, a decent pipe and a variator at the verry least to get anything out of a 50 enigine
a nice 21mm carb on a polini sport cast iron 70 kit with a lazer x pro a variator and a gear up thts my setup