1970s Proper Carb Base gasket on 70 Deville 472

[Bill Kaufman CLC# 15225]

Howdy from Texas, I have a rebuilt Qjet 7040230 that I assume is the original to my 1970 Deville. I am putting it on the factory intake # 1495955 that I also assume was original on the 1970 472. ( the engine was rebuilt years ago so I can only guess its originality) I am trying to fix a major Vacuum leak around the base of the Carb. After a little research I have noticed that Cadillac changed the 472 intake manifold carb exhaust ports from year to year , smiley face design etc...  My Intake does NOT have the "Smiley face " but the picture in my 1970 Factory Service Manual states that all 1970 Cadillacs came with the cross over passage ( Smiley Face). While searching for the proper Base gasket several types and designs pop up up as the correct gasket. Can anyone help me with which design would seal my QJET to my intake. I ordered the Felpro R4 60098. It fits but seems to barley seal around the large ports. It also has a slot cut out in both primary holes. The Throttle base has no slots.  Thanks !

[Daryl Chesterman]

Looking at Mike's Carburetor website for your specific carburetor number, it shows two possible base gaskets—both different in design and thickness!!!

     https://www.carburetor-parts.com/search.asp?keyword=7040230

It might be worth a call to see what they think is the correct one.

According to this webpage, your carburetor number should be the correct one for your car.

     https://www.thecarburetorshop.com/Kcadillac2.htm

Daryl Chesterman

[klinebau]

The '70 intake manifold does not have the open "smiley face" crossover passage.  It does have an internal crossover passage to give heat to the carb, however.  The base gasket has four holes, is relatively thin and looks like G729 from the link above.  Using a thicker gasket can be used to seal a problematic carburetor, but will require the divorced choke to be readjusted.

[Bill Kaufman CLC# 15225]

Thank you Kurt and Daryl, The links are very helpful. The Heat proof (thin) gasket I received from Felpro is the exact design of the G729. It has the two slots cut out in the primary holes. I wonder what that is for. The base has no slots. You also mentioned that I could go with the 1/4" gasket of the same design for better sealing capabilities. That may be way to go for this project. Anymore tips or tricks I should address while doing this ? Thanks again, your help is very much appreciated !

[klinebau]

I don't really know the purpose of those cutouts.  They seem to allow a passage to a depression/chamber in the intake manifold.  Perhaps something to do with allowing heat to carburetor?

You can put a straight edge over the carburetor base to determine if the baseplate/throttle body is warped.  Warpage can be corrected by putting the baseplate on a belt sander, but needs to be disassembled first.  I have learned a ton about the Quadrajet from Cliff Ruggles (https://cliffshighperformance.com/simplemachinesforum/) and buy all my parts there.

["Cadillac Kid" Greg Surfas 15364]

How about a shot of the intake and the carb bottom?
Greg Surfas

[Bill Kaufman CLC# 15225]

The Cliff's web site is very informative.. Thanks !  I installed the thick 1/4" gasket and that seemed to cure the vacuum leak. The new thick gasket does not have the Mystery Slots. I have attached a pic of my Intake. Before installing the carb I carefully compared my base to the picture of the base shown in the 70 service manual. They were identical. I have attached that throttle body picture. I plan to let the gasket set and compress for a few days then re tighten to spec.. What do you suppose is the purpose and the importance of the 10 ft lb on the front bolts but 14 lbs on the rear bolts. Just curious. Thanks for everyone's help.

[Chopper1942]

The long front bolts go through the carb bowl cover, float bowl, and base. If the front bolts are over torqued, they will cut the cover gasket and distort the cover and float bowl. I have seen many Q-Jets damaged by over tightening the front bolts. Many of the thicker gaskets have a hard spacer to prevent gasket damaged if the rear bolts are overtightened. The only thing overtightening the rear bolts does is chew up the aluminum base.