The NSR150SP is sadly a rather underpowered piece of kit in standard trim.

You need a pipe to stand any chance of getting power, but seeing as you're in Singapore you wouldn't get out of the parking lot without losing your bike to the local cop shop!

Basically, there's very little you can do to the 150 to get more power if you don't change the pipe, or at the very least cut it open and throw away the silly cat inside it. While you're there you can shorten the pipe (25~30mm will make a good difference) in the belly section. Then weld it up again and tell any inquisitive copper that you had to cut it open to clean the rust out from inside.

A bigger carb will help. It doesn't add huge amounts of power, but does let it rev out more freely, so it won't feel so strangled by the ridiculously small 26mm carbytooter. 32mm is a good start, or if you're feeling a little more rich you could opt for a PJ or a PWK and go bigger.

Don't go too big on the carb though unless you're going to open the engine up and start porting and modifying the crank cases, as the ports and intake are designed for bottom/mid range power. Hence the tiny carb as standard.

You can get up to around 30hp without too much trouble. More than that requires porting. They can get over 40hp if you've got the time and money!