actually half my question belongs here and the other half on the engine forum.. but i couldn't split it in 2  :)

i have a holley 1020 carb  and wondering about the vacuum connection on the carb:



at point (A) all major vacuum lines are connected to this one
point (B) goes to vacuum on ignition

point (c) not connected to anything.. but what is this one for ?  ( when i take off the cover on it my idle goes up )

if i disconnect hose at point (B) no change in idle .. while i thought it would give an vacuumleak which made the engine run rougher??

now i come to my main question while i got onto this carb question.

on my valve covers are on both sides those " mushrooms"  for "airvent" :




today i was told that it is wrong to have those on both sides... i need to have a valve plug installed on one of the 2 valvecovers and that valve connected to the vacuum on my carb :




why is this needed.. and how " bad" is it not to have it like this , i already have installed that "valveplug"   . should i notice any difference when engine is running?
ohh.. and the right connection to the carb is at point (A) ?   and doesn't that suck dirty bit oily air into my vacuum system??


thank you

art-corvette

first off--what year and engine size? only thing i can tell you is the last pic is the pcv valve whhich connects to the carb. if you disconnect hose with car idling and nothing happens the vacuum happens when you rev the engine. a vacuum guge will show you.

it is a 1978 350 L82 block
uhh yes.. on the last pic.. that pvc valve i got today

but what is that  pipe on first pic  (point C) for.. when taking cover of i can feel it sucks vacuum right away  ( and idle goes up)




art-corvette2007-04-28 15:09:44

What there are talking about, it sounds like, is the engines Positive Crankcase Ventilation system (PCV valve for short) and yes it is needed.  It uses the  vacume to ventilate the inside of the engine. Basically it allows fresh air in one side and sucks out the blow-by (and other fumes) back through the carb to be burned off in the cylinders.  Without it the engine will start to buildup deposits inside and eventually blowing seals and leaking oil.   I know some of the others can explain it better than I.  As for the vacume ports on the carb, it sounds like what Art-Corvette said, one of the ports is above the throttle plate (port A)  which would give you vacume as you opened the throttle and one is below the plate (port C) which would give you vacume at idle, if I'm not mistaken that is. . . . .

You need the "mushroom" vent on one side, and the PCV valve on the other side. The PCV valve should be connected to the rear of the carb, at the large fitting normally located there. Port "A" is not large enough to work correctly for the PCV system. It needs a "dedicated" fitting. If your carb doesn't have the large fitting on the rear, you may need to put one in your intake, if there is a place for one.
Port "B" is for your distributor vacuum advance, and there should be no vac. there at idle. If you give it some gas, you will feel vac. there.

As far as the port "C", does it have vac. at idle or not? If you don't need it, then it should be left plugged. This is not the orig. carb, and so, it is configured to work on several different applications, some may need the extra fitting(s), some may not.Adams' Apple2007-04-28 17:59:05

I dont know why so many people do that crap with venting both sides...

thanks guys for all replies.. things got clear to me now. even answered a question before i could put it on here : about the port on the carb doest look  large enough to have any effect. .

but .. i wouldn't be me if i didn't got another question afterall

i found a port on my intake.. it is a bit larger then the one on my carb.. but would this be large enough...or... can i combine the pvc valve with the port on my carb where the powerbooster is connected to...or is this very forbidden?
art-corvette2007-04-29 04:57:47

you should be able to combine it with the power booster..

The PCV valve needs to be connected to full manifold vacuum. It won't work correctly if it is connected to a ported vac. fitting. This is why they are always connected to the large fittings on the carb, or intake. You may have to "T" into the line for the brake booster(large hose in above pic) to get the PCV working.

thankz guys... now i know enough to fix this situation