Rochester Quadrajet (on a '67) question

[Julien Abrahams]

Hey guys, I have figured out where I had a vacuum leak. It looks like I have a wrong gasket. I am not sure whether the throttle body to float bowl gasket or the float bowl to airhorn gasket is to blame. When I use the gaskets that came with the rebuild kit, I have a huge vacuum leak at the side of the choke pull off. I´m not sure how this is suppose to work. Because when assembled, it draws in air through the opening where the choke rod comes up (to connect to the choke valve). So there is an internal connection between the vacuum connection of the choke pull off and the opening for the choke rod. I 'fixed' it by using paper gasket material to close off the hole at the bottom of the throttle body. Ofcourse now the choke pull off has no vacuum anymore. Does anybody have an idea where the problem lies?
Thanks in advance.
Julien.

[TJ Hopland]

Did your kit come with several gaskets?   What usually seems to happen is that someone in the past used the wrong one and you just matched the same wrong one up again.  There may be a hole in a completely different spot that gives the vacuum to the choke.

The 67 has a vacuum choke on the carb?  I thought the Rochester Cads had the choke well in the intake till they went electric in 75?   Maybe you have mutant custom carb made from lots of parts?

[Chris Bryant #19358]

Dear Julien,

I think Mr. Hopland is on the right track. There many versions of the Quadrajet and in my experience of rebuilding them, you have to be VERY careful matching up the gaskets. There are probably websites where you could do research on exactly where the carb came from by using casting numbers. Some also came with a little metal tab with numbers on it if memory serves. The tab was imprinted with a serial number on it.

I hope this helps.

Chris Bryant #19358

[Julien Abrahams]

Dear Bryant and Mr Hopland,

That would be a logical explanation. I got the rebuild kit from a guy that sells Cadillac parts here in the Netherlands (second hand and new parts). I'm not sure whether it is the original carb that came with the car, and how many times it has been opened up in the last 40+ years. In the shop manual however, it says that the choke pull of is indeed vacuum operated. Also the carb number says that these carbs were used on 67-69 Cadillacs and on Pontiacs.
I've looked the rebuild kit up on the Quadrajet Parts website (using the carb number), and it appears that the kit contains the same gaskets (although I also take into account that they probably won't take a picture of each and every gasket in the kit for all the kits). In the coming weeks I will order a new kit from Quadrajet Parts using the carb number. It runs now, and I first have to go through the bi-annual inspection (here in the Netherlands the inspection is only once every two years for cars which are 30 years or older). Thanks for the tips. .

[TJ Hopland]

Ya at 40 +years now its hard to know how many people have worked on things like carbs and what they may have done.   That is where its nice to find a good carb shop that has seen 100's or 1000's of them.  Those people can just look at a carb and know what car it came off and what gaskets it needs.   When they open it they can spot modifications or wrong parts.   Finding a shop like that in the USA can be difficult so I imagine out of the USA its even worse or even flat out impossible. 

There is also the possibility that over the years the people who make the gaskets have screwed up.   There may be a hole that is or is not supposed to be there on one of the gaskets and somehow when translating paper drawings to CNC programs they made a mistake and know it but they looked at how many apps actually require that gasket or hole and figure it was not worth the time it would take to correct the problem.   That error could have happened 20 years ago and since then 10 other manufactures have just copied the bad design so now that has become the only gasket available.   I have seen that sort of thing a lot lately with how often companies change manufacturing methods or just simply change owners and then now days with so much production moving 'offshore' with the goal be lowest production cost possible things are just getting worse.  Look at how many components they can't quite seem to get right for new products, you really can't expect them to get things right for a niche market like 40 year old cars parts. 

I don't have a manual from that era but sometimes I think when they say choke pulloff they may be referring to one of those vacuum actuators on the side of the carb.  Depending on the year and model there could have been as many as 3 of those. 

The choke spring / thermostat / heater usually completely closes the choke when its cold which is what you want for a cold start.  As soon as the engine starts (generates some vacuum) there has to be a mechanism to allow it to immediately open slightly.  Sometimes this is done with a weight balance thing and slots in the linkage so the blade closes by gravity but as soon as there is a vacuum on it it tips open slightly.  Other designs there is one of those external vacuum actuator things that pulls it open slightly.  After that is when the heating action continues to allow it to open over the next several minutes.

How that choke coil gets heated is another variable.   On the inline engines the typical design was there was a round bowl like thing on the side of the carb that contained the coil.  There was a vacuum passage from that into the carb so when the engine was running there was a draw.   There was then a metal tube that went to a 'stove' on the exhaust manifold.  It was not actually drawing exhaust, it was just a passage through the hot metal so it was actually drawing in 'fresh' heated air.    On many of the V8's there was a exhaust passage through the intake manifold (even before things like EGR valves).  They would put that little 'stove' in that exhaust passage and there would then either be a short tube leading from this stove to the bowl thing on the side of the carb or they would just mount the coil in this stove and have a rod that went up and operated the various levers and such on the carb.   I know earlier 70's Cadillac's were this style.  I think Chev often had the design with the stove in the intake and the short tube.  In 75 many of the makes including Cadillac took the inline/chev design with the bowl on the side of the carb containing the coil and instead of having a connection to a heat source to draw in heated air they just added an electric heater to the little bowl cover.   I believe they often still left the vacuum source there but there was no inlet so it didn't do much.  On many of the models there was still a nub in the bowl casting for the tube but it was not drilled or threaded so at a glance it often looked like something was missing.   In many cases you could just add a heated cover to a tube version and or the other direction, you could find a bowl that was drilled and mount that on an engine that had the stove.  Carter, Autolite, Holley, Webber all seemed to have very similar systems on and off over the years.  Where swaps got more complicated was with the style where the coil sat in the intake.  Also could cause problems with the thickness of the gaskets because that changed the length of the rods.  You could bend the rods within reason to accommodate typical gasket variances but where it was a problem was if you wanted to try and use a extra thick gasket or some sort of insulating plate to try and alleviate vapor lock issues.       

[dsrour]

Could it be the metal shim  that goes on intake first and covers the exhaust crossover system? Its a common mistake to put gasket on first and then shim, or to leave out shim. The hot exhaust gases quickly burn through the fiber gasket.

[TJ Hopland]

I suppose that is a possibility.  I remember reading about that issue with the earlier 472 and 500's so it would make sense that the 67 had that open exhaust port in it too since it was apparently a test bed for some of the 472 stuff like the Q jet and rocker system.  I know that port was gone by the time EGR came in which I believe was 73.  I worked on a 72 not too long ago and I don't remember that having that open port or an EGR so I don't know when they made the change. 

[The Tassie Devil(le)]

The shim gasket is not used in 1972.

Bruce.

[dsrour]

I thought it was 67, first year of Qjet, and would have metal shim.

[TJ Hopland]

So it was used 67-71?

["Cadillac Kid" Greg Surfas 15364]

The '67 QJ takes not only a eunique (to that year) gasket kit, but also the base gasket is different. No SS shim on the QJ.
Greg Surfas

[TJ Hopland]

Was that unique gasket because it was not a truly new intake to fit the QJ?  Perhaps because they knew it was a 1 year only thing they just made minimal mods to the intake to make it work?

So the earlier 472's did not have the metal piece in the gasket stack?  It was just one of those metal like gaskets like an exhaust manifold?

["Cadillac Kid" Greg Surfas 15364]

TJ,
The '67 manifold base and carburetor were different than the later ones. They changed in 1970.  It wasn't a "Cadillac thing" but a change in the QJ configuration and development.  The QJ had an iron base and had an exhaust heat passage directly in the carb base, so the shim was not required for protection.
Greg Surfas

[cadillactim]

The 67 quadrajet does use a stainless shim, and I know the 68 did also, not sure about 69 without checking the parts book.

I've rebuilt both 67 and 68 quadrajets and they use the shims.  I've even seen a 68 without the base gasket, just the shim between the carb and intake, and it ran fine.

The 67 and 68 intakes have a much wider base gasket than the 70s. The kits I've bought have all the proper gaskets, including the wide base gasket.

I know 67-69 Cadillac quadrajets are basically the same, and can be effectively interchanged with little or no modifications (choke linkage, throttle linkage may need swapped out). I think the CFMs are pretty similar.

Tim

[Julien Abrahams]

Well, just to get it running and to see where the problem actually lay, I custom made a base gasket from gasket material which should hold at least for a couple of minutes. I also made a mod to the throttle body/float bowl gasket (blocking off a vacuum passage that somehow got connected to the area where the choke rod comes up) and then she ran fine. Much smoother, no hesitation, great response. I did not connect a vacuum line to the choke pull off (which normally also holds the air valve of the secondaries to prevent bogging). When I floored it, I didn't notice any bogging and she pulled good. Although it wheighs almost 2.4 tons, it goes forward quite well .
After a couple of heat cycles though, she began to idle badly again, and I suspect it is the custom base gasket. I suspect that it blows exhaust through, messing up the primary port mixture. I will order a new kit somewhere over the next days.
And about the metal shim: the manual states that the gasket goes on the intake first, then the metal shim and then the carb.
In the mean time I need to do some work on the brakes as well, so I'm keeping busy .

[The Tassie Devil(le)]

Yes, the shim goes directly under the Carb.

Now you have it running badly, it would be time to pull the carby and inspect the home-made gasket and see where it had "collapsed".

Bruce.

[cadillactim]

The Felpro base gasket number is 60010.  The Victor-Reinz gasket number is G14130.

Make sure your heat riser is not stuck closed and causing excessive heat under the carb, thus burning a hole in the gasket.

Tim

["Cadillac Kid" Greg Surfas 15364]

Gentlemen (and ladies if you are out there),
I stand corrected.  I know that I ran a QJ on my '66 using a '67 intake and QJ without a shim.  This discussion reminded me that I did so successfully because I had "JB welded" the exhaust passages at the carb base.  Not necessarily recommending that , but in southern Texas, the extra heat to the carb base is not missed. Tim has the correct Felpro number and they still should be readily available.
Greg Surfas

[Julien Abrahams]

First of all: thanks guys for all your responses, it is highly aprreciated!
The heat riser valvle is not installed anymore (somewhere in  the past it was replaced by a spacer), so that cannot be the issue. The gasket appeared to be OK. I checked whether it had a vacuum leak by using brake cleaner and I didn't find any. As I have some other projects as well, I'm just going to order a new rebuild kit from Quadrajetparts, and then I'll take it from there.

[dadscad]

Hey guys, brake Cleaner is the wrong thing to use around heat, flame or welding. It can produce a deadly Phosgene gas that only a tiny bit, if inhaled, can cause serious illness or worse, kill you.