I have a question: on my intake manifold there is a drilled and tapped hole for 1/8 npt and previously it served to power the wipers, provide vacuum for the vac advance and then around 1980 I added a third nipple to power a wolf whistle. Is this 1/8 npt hole going to be large enough for an effective pcv system or do I need to make it 1/4 npt? Or larger? Obviously adding pcv is going to lean the fuel/air ratio and obviously larger means leaner, so what say you folks? The pcv valve wants 3/8 inch hose, but a 1/8 npt connection is going to reduce that by over 50%.
Actually I have 2 questions and the second one involves an alternative approach. In Briggs & Stratton engines, crankcase vapors are simply sucked back into the engine via a pipe which connects to the crankcase and then enters the throat of the carburetor right below the air filter. There is a simple check valve to keep it from becoming a bomb in case of a backfire. The ID of the pipe that sucks the vapors in is 3/8" and that is for a one-cylinder small engine. So the crankcase vapors, water, etc go in to the carb along with clean air, are mixed with the fuel and then burned during combustion. Why would it not make sense to modify the road draft tube and then connect it straight to the air filter (inside the air filter so these vapors won't foul it) and use a pcv valve as the backflow preventer to protect in case of a backfire? The effect would be the same (that is to say you'd still be burning crankcase vapors and water vapor) but the air/fuel mixture would only be modified minimally. If you wanted, you could also easily add a common water separator (the kind used on air compressors) and you'd remove water and maybe other water soluble junk. You'd probably have to empty this frequently, however...at least I'd expect you would if you lived in a humid area. Ideas?
