Thread: carb gaskets

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do you only use a 4 hole gasket if you have a 4 hole intake?
my intake has a big square hole, and I thought it was a dual plane, but I looked last night and the middle divider has a square cut out of it. What's the deal with that?
Also, my carb has some channels on the underside at various places. Should these be covered up by a 4 hole gasket, or uncovered by a square hole open gasket?
One more thing, there is a big hose connection on the back, is that for a pcv?
there are also two other ones. One leads into the primaries with some channels that I think is for the dist.
The other I can't tell, it has a tube on it now with a bolt stuck in the end, what would that be for?

Generally you would want to use a 4 hole carb gasket on a 4 hole intake. What carb and intake setup are you running?? Usually the large hose connection on the back is for power brake booster, should work fine for a PCV valve also.

Dave---are you sure about the vacuum line for the power brakes being o.k. for a pvc? I have been told that a power brake vacuum canister is a sealed unit with a check valve on the infeed line, so that effectively the vacuum line on the carb can only pull air there freely in the first minute or so after the engine starts, then once vacuum is created in the canister, the carb can't pull any more air there untill the brakes get applied, or the vacuum in the canister bleeds down while the car is setting with the engine shut off. If you use it for a pcv line, the carb will pull too much vacuum at that port all the time and cause the carb to behave like it had a vacuum leak at idle. I heard all this about 3 weeks ago when I first fired the engine in my roadster pickup. I had that brake vacuum port running to my pvc, and the engine wouldn't idle properly. When I plugged that line, the engine idle smoothed out a lot, which lead me to believe there may be truth to it.

where should I go with the pcv then? should that go to the threaded hole in the intake?
does anyone know what the other two connections on the carb or for, they are smaller tube inlets.

See my thread---"quadrajet questions"--there are a whack of people smarter than me around quadrajets that tried to help me out. One vacuum line is for the distributor vacuum advance----one is for the modulator valve on the automatic transmission, and hopefully one for the pcv system.

Brian, your explanation makes sense, but I can say I have had my pcv hooked up to that port w/ the power brakes (tee'd off) for years, and I have no issues that I can tell. Anyhow, Tcodi, the two small vacuum connections on the front or sides of the carb are full time vacuum and ported vacuum...the full time is the one in the base plate, or nearer the bottom of the carb...the ported works with the throttle, and varies with engine speed...either will hook up to the vacuum canister on the distributor, and there are many arguments about which to use...you will hear both arguments. I use the full time, but I tell people to try both and see which works better in your particular application. And yes, you can hook the pcv up to the threaded connection in the intake. The divider in the intake plenum is cut down to make if work a little more like a single plane intake. That is sometimes done by hot rodders...it lets the air/fuel mixture cross over to the other intake ports without following the runners as directly. It's supposed to make the dual plane a little more high RPM friendly. But with todays intakes, they work pretty well as manufactured. It's an old fashioned way of modifying something, like drilling the throttle plates in a carb so it will idle with a bigger cam. If your intake has a divider in it at all, it is a dual plane...an single plane is all open inside. John