Dave, You are right ontrack to be concerned about change in mixture when PCV is added because the engine is being fed air without the carb adding fuel.
Well, some fuel is added--the combustion blowby is fuel as is oil vapour that is carried over from the crankcase and there is the fresh air being inducted from the vent--but nothing is controlling all these variable sources.
And then there is the concern about where it is added to the induction tract.Is the inlet to the manifold on a runner to a cylinder pair or in the plenum below the carb? This can effect the mixture to a cylinder or pair.
So with an added on, not engineered PCV, we many times have compromises that can adversely effect engine life and performance.
I have many times questioned the wisdom of OEM placement of PCV entry into the inlet tract as some are notoriously horrible at plugging when the engine is older or the results of minimal maintenance of oil is overloading the air flow design.Ford 302 comes to mind.
Done lots of valve work with my eyes and mind open and I never saw the port and valve pluggage with coke (carbonized oil and ???)before PVC that we did after.Of course that changed again (for the better) with the coming of port FI because the valve area is sprayed w/fuel on each shot, and the inlet valves are much cleaner now.
Cleaning up for head work by manual methods can be a real lesson in carbon buildup in the engine.
