Chevy 350 motor with a two barrel carb on it i changed it to four barrel carb do you ned to change the camshaft also?

No, you don't "NEED" to change the cam, but it depends on what you're trying to do.

You can pick up some torque by changing the cam but you need to be careful. If you go too far the engine will start to idle rough and you'll loose fuel economy.

An RV cam will give you a little extra low end torque and at the same time can slightly improve the fuel economy. That might be helpful now that you have the 4-barrel.