Quadrajet Compatibility - '67 and '68

[cpiel]

Folks, I have a '67 Deville that uses Quadrajet Carb # 702723.  It took me a long time to get this carb running right and I have been told GM had trouble with these and the carbs on '66's.  At Carlisle, I came across a vendor who specializes in carbs who has a Quadrajet for a '68 (#702823), and he said this unit would be compatible for my '67 429 despite the fact that '68's were 472's.  He said the '68 unit was redesigned to deal with some of the issues with the earlier carbs.

Before I buy this unit as a spare, does anyone have any advise or expertise they can share here?

Thanks
Chuck Piel

[Dave Shepherd]

I would say the metering parameterrs would be different based on
Just the inncreased air flow required by the 472, try and research jet and metering rod specs between the two. Also internal passages could be different.

["Cadillac Kid" Greg Surfas 15364]

Chuck,
I put an original '67 QJ on my 66, making the motor essentially a 67, and after a thorough rebuild, shaft (re) bushings, and well plug seals, the carburetor was seamless.  The QJ was used on just about everything, and most of the engine size differences were accomodated by secondary air valve opening restrictions and idle passage changes.  You said your car is now running right.  Why change?
Greg Surfas

[Scot Minesinger]

There were changes between the 67 and 68 carbs, and the 68 carb may allow the 67 to run and drive.  However, since there is not a shortage of 67 carbs anymore than a shortage of 68's, I would not install a 68 carb on a 67.  There is enough of that going on without consent or knowledge by the owners unfortunately.  To knowingly do this will not be good, say for example the choke mounting and linkage is different, due to different intake manifolds.  Look around for another 67 carb as a spare.  The carb guy is not as renowned as he thinks he is or he would not advise doing this.  Each carb from 67 thru 70 was slightly different and a sure sign of trouble is someone who thinks they are the same.

["Cadillac Kid" Greg Surfas 15364]

Chuck,
This thread made really needs a definitive answer as to what the differences are between the 67 and 68 QJ.  Now first of all there were 5 different Q J's used in 67.  Cars  (except the limos) used the same carb with or without A.I.R.  In 1968 there were 8 carbs used across the models and years.  There is by the way one more number for your carb.  It should be 702723 (0 through 5 for the last number).  The 4 numbers under the carb number are the date of manufacture, which would indicated whether it is a late or early production, because there can be a difference there.
That said, given a single carb number for both years, say for standard AC models, the last three numbers would be 231.  Between the two years, 1967 and 1968 there is a change in primary and secondary rod sizes.  This essentially opens the fuel system up to accommodate the larger engine, and corrects the fuel curve for the newer engine.
Confusing? Yes it can be especially for the mechanics new to Quadrajets and their operational characteristics. 
The short version of all this is again, IF your '67 carb is functioning well, not leaking, not stumbling and giving you the 10-12 MPG the 67s were intended to give KEEP IT.  Fuels are chemically much different than they were in 1967, so actual performance is what you should judge your carb by.
By the way the "big problem" that early QJs experienced was fuel bowl plug leakage and engine fires.  If yours doesn't leak it would be a valid assumption that this has already been corrected as there were recalls on them even back then.
Hope that helps.
Greg Surfas

[cadillactim]

I've had experience with 67 and 68 quadrajets. TECHNICALLY, they are a little different as noted, but in real world driving, the 68 would do fine on a 67. The base plate on 67-69 are the wide base, but on 70 that changed. Minor differences like choke linkages are easily switched.

BUT, the 68 suffers from the same problem as the 67, the brass plugs leaking. From what I have read before, in 69 they somewhat improved the plugs, which are more easily fixed. The 67 and 68 carbs are more difficult to fix the leaking plugs because of the thin walls around the plugs.  A 69 carb would be a better switch than a 68.

So in the carb's guy defense, he is correct saying the 68 will work on the 67 in the real world. However you aren't gaining anything in regard to leaking plug problems.

Tim

["Cadillac Kid" Greg Surfas 15364]

Tim,
JB weld when properly applied works wonders for bowl plug leakage.
Greg Surfas

[cadillacmike68]

Tim,
JB weld when properly applied works wonders for bowl plug leakage.
Greg Surfas

Where do you apply it?

I have either leaking bowls or just plain old fuel evaporation. If the bowl plugs are leaking, I might as well close them up.

Chuck, how much does that vendor want for the 702832 Q-Jet? I might be interested. You can PM me

[Scot Minesinger]

It is understood that the 68 carb will work on a 67 Cadillac.  However the carb installed works as per the initial post.  I would not change it.  If the 67 carb ever fails it can be repaired/rebuilt.  If you want a spare get a 67. 

The problem is for whatever reason someday that car will end up in another owner's care.  When it requires repairs 67 carb parts will likely be purchased and they will not work as well if a 68 carb is on there.  That is the big problem with these carbs is different year parts mismatched. 

Granted this can be kept straight by the number on the carb itself, but why risk all this hassle?

[Gene Beaird]

Tim,
JB weld when properly applied works wonders for bowl plug leakage.
Greg Surfas

Any decent epoxy-based adhesive will work.  I use regular 2-part epoxy on my repairs.  Just make sure the surface is clean.

[Dave Shepherd]

Any decent epoxy-based adhesive will work.  I use regular 2-part epoxy on my repairs.  Just make sure the surface is clean.

Slow set JB weld work good.

[Julien Abrahams]

Just to chime in and ask a question .
On my '67 there was a '69 Quadrajet when I bought it. It ran OK. But when I discovered that it was pretty badly warped I searched for a replacement. I found another Quadrajet, but it was from '67, so should be correct for the car. I only changed the throttle body (as it was different from mine) and the car idles well, and runs good. Because the throttle body was different, I guess that the '67 came off a different car (maybe a non-airconditioned, or maybe not even a Cadillac). It worked for me.

As for the leaking fuel well plugs: how can you tell if they are leaking (without taking the carb off)? Just curious. I thought about it as my '67 Deville needs to turn over a couple of times (say crank it for about 6 seconds) before it will fire up. This is after it has been sitting for a week or 2. I thought it might be leaking well plugs which would cause the carb to drain over a period and explaining why it takes a bit longer for it to fire up (as the pump first needs to fill the carbs fuel well.

[Scot Minesinger]

The more cranking after the car sits for more than a day or two is a symptom that the plugs leak.  I just live with it.

[Viator Trudeau]

Hello,,  my '68 & '74 eldo float bowls will empty them selves in a week or two.I have always felt all that cranking to fill the bowl is a lot of ware on the starter and ring gear,  so I use a Qt. bottle of gas W/ a 6" length of small I.d.hose into the front carb. vent to prime W/ a few oz. of gas.  Replace the A C cover and it starts on first stroke.

V.Trudeau

[cadman56]

Let me open up a real can of worms here.  Now, be nice when you bash me.  What about replacing the carb with one of the aftermarket bolt on throttle body fuel injections units I have seen?
L. Blanchard #5820

[Scot Minesinger]

cadman56,

I think you have to change the intake manifold, not sure one is made for a 429 Caddy engine.  Fairly certain that since the 472/500 block is popular and more than a million were made, bolt on fuel injection may be available.  Plus it was available as an option in 76 (maybe 75 too not sure).  I have a fuel injection intake manifold for a 472/500 engine, yet to maybe get installed one day on a non-original car yet to be pucrchased (made that way before I bought it).

The 472/500 fits without too much trouble in the frame mountings intended for a 429.

Not sure the initial post wanted to go that far?

["Cadillac Kid" Greg Surfas 15364]

With all due respects, this discussion was regarding interchangeability between 1967 and 1968 carbs.  How on earth did we get here? 
Greg Surfas

[cadillacmike68]

Let me open up a real can of worms here.  Now, be nice when you bash me.  What about replacing the carb with one of the aftermarket bolt on throttle body fuel injections units I have seen?
L. Blanchard #5820

Pure Blasphemy! 

If you want to, fine. I just installed a small inline Airtex electric pump and if the car has been sitting I just run it for 10-12 seconds before starting the car. You can leave it off when the car is running because it is a flow through design.

[Julien Abrahams]

Yes, that is an idea I have been playing around with in my head as well. However, I am not too bothered by it. Not so bothered that I want to take off the carb again. So I let it be.
Also, on the plus side: this way you can already get oil pumping through the engine and create oil pressure before it actually starts up.