Smoke coming from breather

[540slant6]

I agree with your assessment. However, I temporarily piped a breather with a nipple into the air cleaner. The idle instantly slowed down like the fumes were choking the carb.......I'm going to try and post a video this weekend.

 

[nm9stheham]

I think there is another piece to this puzzle. It seems your pcv is working, but the breather is open to the atmosphere and not hooked up to the air cleaner, like it should be. See picture.

This would not cause the symptoms that the OP is seeing at idle and low throttle settings; the non-PCV breather is connected to the air cleaner for 2 reasons:
- It may have a small filter up there to filter air being drawn into the crankcase at idle and low and moderate throttle openings, or will use the main air filter to filter the crankcase air (This the situation shown in plumkrazee's illustration.)
- At near-WOT and WOT, the PCV has no real vacuum to work with below the carb so this upper breather hose becomes the path for the crankcase vapors to be pulled up into the air cleaner and then down into the carb at WOT. (The crankcase vapor flow is reversed through the hose to the air cleaner.)

As for testing vacuum on the crankcase side of a PCV, I don't know of such a test; it has to flow at a low level with a high vacuum on the crankcase side....maybe someone else knows of one. You should be able to:
- blow through it from the crankcase side as well as the hose to the carb base;
- put your finger over the crankcase side of the PCV and see if you feel a vacuum at idle, then pull your finger off and see if the idle does not drop any large amount