A PCV is a pretty carefully calibrated air leak. It has little, if any effect on mixture, and the benefits far outweigh the disadvantages. For one thing, a "closed loop" PCV system approximately doubles the life of piston rings and other components by dramatically reducing the amount of road dirt the engine ingests, compared to the road draft system. It also eliminates corrosive crankcase vapors far better than road draft, and for the tree huggers out there, it's rumored to reduce air pollution. Any alleged mixture changes can be compensated for by changing carburetor jetting and/or power valve calibration, assuming you have something like a 4-gas exhaust analyzer and a chassis dyno to be able to accurately monitor the results of your modifications. Have fun!
Jerry

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