[Offrhoder4x4]

You've got too much crankcase pressure. Check to make sure your PCV valve/s aren't clogged, lines from the PCV to carb run correctly or clogged.

My 351 did that after a rebuild even with the lines run correctly and everything looking good. I eventually had to let one of the PCV's evacuate directly to atmosphere.

 

[Offrhoder4x4]

You'll have to play with it a little and see what works for you. My 351 was supposed to have both hoses going to vacuum on the intake, but it wouldn't run right. So I put one to the intake and one to the atmosphere. If I plugged one, it would spit out the dipstick.

My bro's CJ on the other hand, can have 1 plugged and 1 to the intake and it's fine.

Just move the lines around till you find something that works for that engine, but ideally, you want both PCV's going to vacuum.