Assuming this is a B&B type pump.

Are you sure your plumbing is correct? There should be no check valve from the engine to the pump diaphram. There should be a check valve from the pump to the muffler.

The muffler pressure may be de-priming the pump if you don't have the check valve installed. If this is your setup, are you sure the check valve is pointing the right direction - it should allow flow to the muffler and block it from the muffler.

Make sure you have a large enough line from the engine crankcase to the pump - on the order of 3/16" to 1/4" inside diameter.

These systems put out great smoke when set up properly.

Also, you shouldn't have to enlarge the nipple orifice. Most folks have to limit the oil flow to the muffler with these systems. A wheel collar over the tubing works well for adjusting the flow by pinching the tubing with the collar screw.