I have an 88 cherokee with 4.0. When I rev it up it smokes badly, but not at idle or just driving. Anyone have an idea what is wrong?

what color is the smoke?

White when you push on the gas, then black when you let off

Odd. White smoke generally indicates that you're getting water in the cylinder. How's your coolant level? Check your oil, does it look normal? Water in the oil makes it look more like a milkshake.

Black smoke generally means too much fuel in the cylinder.