Quadrajet install gasket help!

[A 68 Wreck]

I have a 68 C20, stock 327 intake manifold, and Quadrajet 4 barrel (7042220).
I need help determining the gasket/heat shield/spacer set up.
1) The manifold has a channel across the front of the primary holes, the gasket has a cut out for that channel, but the heat shield does not? Huh? I know the heat shield sets on the manifold first, so why the cut out in the gasket?
2) The Qjet originally had a 1/4" spacer/gasket between to it and the manifold. A carbon type heat sink spacer thingy w/ paper gaskets on each side. Is this a necessary requirement to keep the carb/mixture cooler?
3) Finally, the Qjet underside, towards the very front, has a small channel. It is isolated from the primary ports. Should that be covered by the gasket?
I believe it originally was?
Thanks! (i tried to attach pics)

[Livrat]

You have what is refered to as the "hot slot" manifold.
From the factory they used the gasket on the manifold and the carb bolted directly to the tin shield, This results in the entire bottom of the carb being heated up to the temperature of the exhaust gas, and the setup is highly prone to vacuum leaks.
To solve the problem associated with the hot carb, I add a third gasket on top of the stainless shield. This gasket has to have the same shape as the shield to prevent any exhaust leaks out the driver’s side of the manifold, and the gasket keeps the majority of the heat off the bottom of the carb.

[A 68 Wreck]

vacuum leak on driver side, yes, exactly. i had the metal plate on the manifold first, and then a 1/4 spacer/gasket then my carb. but, the spacer did not cover the very end of that hot slot on the driver's side. hence, a leak coming out from under the metal shield.
1) So, if i understand you correctly, factory had the gasket i have on the manifold, and then the metal shield then, carb??
2) If i read correctly, I should use that gasket on the manifold, then the metal shield, then another gasket that matches the metal shield i have pictured??
3) Should there be a "layer" (shield and or gasket) on top of that hot slot?
4) The channel on the front underside of the carb should also be covered, correct?
5) Do you use the 1/4 spacer thangy.
I appreciate the help much!

[Livrat]

#1.. Yes
#2.. Yes
#3.. The hot slot is normally open to the heat shield with the gasket sealing the sides.
The purpose of this “hot slot” was to run hot exhaust gasses under the carb to provide fuel pre-heat on cold days. The hot gasses would heat up a stainless steel plate, and the carb was bolted directly to this stainless plate for good heat transfer.
(A hot carb with hot fuel may run very well on cold mornings in Minnesota, but this arrangement does not run well on hot summer days in Southern California)

#4 Yes..
#5, I believe the 1/4" spacer you are refering to is a normal OEM style 71-80 Q-jet gasket. I run those were appropiate.
like this.. http://www.amazon.com/Fel-Pro-60255-.../dp/B000C2G79E

You should use a thin composition gasket that covers the entire bottom of the carb plate
One like this one:
http://www.eraceware.com/mr-gasket-c...pk-115246.html

[A 68 Wreck]

great info. i think i am getting it.
however, towards the back center of the carb base surface there is a "pocket/slot" that matches up w/ the holes towards the back of the shield and gasket, and also appears to line up w/ the channel between to 2 secondary holes in the manifold. The gasket that contacts the carb that you suggest does not have that hole.
So i guess what i am asking is if there needs to be free access (that hole in that gasket and shield I have)between that back "pocket/slot" on that carb and that rear channel on the manifold.
thanks much!

[Livrat]

From looking at your particular carb I do not think it matters as the pocket/slot you are refering too has slots that extends to both sides below the butterflies which will supply vacuum. that slot just allows vacuum to the center rear port on the carb for hooking up the power brake booster (which looks to have a plug in it on yours)

[A 68 Wreck]

Livrat, u da man.

So, to conclude, I am to understand that the only through access from carb to manifold are for the 4 ports? All else on the carb base can be covered by the gasket, and that hot slot on the manifold can be covered by a gasket, w/ the metal shield in between the gaskets?

Much thanks again.

[Livrat]

correct!! you are most welcome!

[A 68 Wreck]

good Sunday to ya Livrat.

you linked a gasket to cover the entire carb base, and it states it is .625" thick. did you mean this one or the .062" thick one?
i think i will need to replace the studs in the intake w/ that thick a gasket, but that should be no prob.

I also saw some .5" aluminum spacer/heat insulators? useful? overkill?

[Livrat]

Thanks!!
I goofed on that one.. the .062 one is (MRG56A) ideal.
A spacer/heat insulator is probably overkill for your application. but if you decide to go with one make sure you get a "4 hole" one over an open one as you need something to hold the gasket secure over the "hot slot", a phenolic one is a bit better for insulation than aluminum.
http://www.eraceware.com/mr-gasket-c...et-115209.html