I have put a viper straight through exhaust on my NC30, it seems to be running fine, but do I need to re-jet or alter the fueling for it to get it spot on? Only an end can not a full system.

Cheers

I would leave it as is if it's running fine.

Gnereally the pilot screwsmight needsome tweaking to suit the exhaust, but again if it's running well best to leave it alone!