PCV Causing Rough Idle?

[Oldyeller]

I am running a Holley 2bbl Pro-Jection system on my 304. It's idling rough and seems like it's getting too much air. I called Holley and the tech told me that a bad PCV would cause those symptoms.

Sound plausible? Should I just can the whole PCV deal and put a breather on it?

[fifesjeep]

Remember that negative crank-case pressure is Ideal... Just don't have too much vaccuum on the crank case...

[Oldyeller]

So I'm assuming that you think I should stick with the PCV setup. Can you explain why negative crankcase pressure is a good thing?

[tufcj]

Did they say PCV or EGR? An EGR valve that's stuck open could cause rough idle too (assuming you have a factory manifold w/EGR). PCV could also cause it.

Bob
tufcj

[AMX69PHATTY]

If i understand correctly, the PCV is a wieghted poppet valve and
should only open and draw air in under the carb at high engine vacuum.
If the PCV valve is "bad" it allows air in all the time
and dilutes the intake mixture, since it is air coming in under the carb.
The air removed from the crankcase by the PCV is replaced
by fresh air being drawn into the Breather on the Oil Fill Tube,
That's why the the hose to the breather should be filtered air.
A motor with bad rings and a lot of blow by will blow smoke out the oil fill tube
since there ends up being positive pressure in the crankcase rather than vacuum.
Vacuum, or negative pressure, in the crankcase by the PCV helps ring seal
and evacuates blow by gas fumes etc from the crankcase and diluting the oil.

[fifesjeep]

If i understand correctly, the PCV is a wieghted poppet valve and
should only open and draw air in under the carb at high engine vacuum.
If the PCV valve is "bad" it allows air in all the time
and dilutes the intake mixture, since it is air coming in under the carb.
The air removed from the crankcase by the PCV is replaced
by fresh air being drawn into the Breather on the Oil Fill Tube,
That's why the the hose to the breather should be filtered air.
A motor with bad rings and a lot of blow by will blow smoke out the oil fill tube
since there ends up being positive pressure in the crankcase rather than vacuum.
Vacuum, or negative pressure, in the crankcase by the PCV helps ring seal
and evacuates blow by gas fumes etc from the crankcase and diluting the oil.

Perfectly put!