Jump to content

carburetor rochester 4 barrel - 4MC with climatic choke number : 7026240


Recommended Posts


i have a buick riviera 1966 and a carburetor ROCHESTER 4MC with climatic choke

reference 7026240


and i have a hose on this carburetor but i don't know where is the issue of this hose ??

it is on the left side on the carburetor as the picture shows


IF someone knows it will be great for me !


thank you


carbu le mien VERS OU.jpg

Edited by cquisuila (see edit history)
Link to comment
Share on other sites

  • cquisuila changed the title to carburetor rochester 4 barrel - 4MC with climatic choke number : 7026240

Looks like the 90 degree elbow on intake manifold with rubber tube attached is what is in question. Maybe a

vacuum source for headlight doors, or some other vacuum powered device. Is not the choke on other side of carburetor? It looks like the choke plate link is on other side.  A body could disconnect the tube and see what stops working….good luck!


Link to comment
Share on other sites

The Riviera has a number of vacuum operated accessories. This line could be serving as the vacuum source for any or all of them. There should be a vacuum canister that this line goes to first, before then running to the accessories like the A/C or vacuum operated hidden headlights. This A/C vacuum diagram is for a 1965 Riviera, as an example. Note the elbow labeled "Engine Fitting". You should get the correct one for your car, as there are likely differences. I realize you're not in the US, but an original factory service manual should be a priority purchase. Your car could have other options like a vacuum power trunk release, which will also use a vacuum line from the engine.








Link to comment
Share on other sites

13 minutes ago, cquisuila said:

i have a lot of pictures of chassis service manual 1966


it is on the left on carburetor as picture joined and it is vaccum outlet OK



I don't know which "left" you are asking about, as the photo seems to be indicating the line behind the carb, per the circle and question marks. In any case, here's what I see.



Buick vacuum lines.png

Link to comment
Share on other sites

  • 1 month later...


my carburetor is very old (Joint plane corroded by rust) and it is impossible to open the first barell (rust)

and i must change


it is a 7026240 rochester 4mc


is it possible to change with a rochester 7042252  for oldsmobile 72/74 engine 455 ?

it is the same model rochester 4mc BUT there are little difference :

- gas bracket

- out filter


here the pictures


i sawn a cheaper rochester 7042252 to sold !



thank very much you for your answers !

i'm waiting the the specialists ! ;);)




diffrenece 7026240 7042252.jpg

Link to comment
Share on other sites

23 hours ago, cquisuila said:


is it possible to change with a rochester 7042252  for oldsmobile 72/74 engine 455 ?

it is the same model rochester 4mc BUT there are little difference :

- gas bracket

- out filter

Probably, if you (or a friend) is a carburetor specialist, and one of you has a carburetor machine shop.


Personally, I would not want to do it, especially outside of the USA.


You have identified some differences. Others:


External: automatic choke hook-up, carburetor mounting to manifold (you will probably have to fabricate an adapter plate). Yes, the bolt pattern is the same, but the carburetor footprint is different.


Internal: the calibrations are just plain different. The 1972 is a smog engine, the 1966 is not. That carburetor, unmodified, is going to be leaner than Jack Sprat!


Idle tubes, idle air bleeds, main metering jets, primary metering rods, secondary metering rods, vacuum piston spring, and probably the secondary hanger will all require changing.


I would look for a 1968, 1969, or 1970 Buick carburetor (no, I don't have one for sale).



Link to comment
Share on other sites

  • 3 weeks later...

I JUST received my refurbished carburetor 7026240



it is transmitted with 2 gaskets : one high-temp composite gasket and one stainless steel shield

i think that i have to put the composite gasket on the intake manifold then the stainless then the carburetor ...is it exact ?


I SAWN THIS fitting here https://www.corvetteforum.com/forums/c1-and-c2-corvettes/1978466-q-jet-carb-base-gasket-tech-info-the-hot-slot-manifold-problem.html


A common mistake when installing a Q-Jet on a 1966-1970 GM V8 is that the “mechanic” uses a 1971 – 1980 carb base gasket. This results in severe exhaust gas ingestion into the intake manifold, external exhaust leaks on the driver’s side of the carb base, and possible carb base damage and engine damage from detonation.
Early Rochester QuadraJet Carburetor installations (1966-1969) often used a “hot slot” exhaust groove that runs from side-to-side in the intake manifold just forward of the primary throttle bores, popularly known as the “smiley face” manifolds. The purpose of this “smiley face 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. Chevy used this design on ’66-’68 327/300hp, ’68 327/350hp, and ’66-’69 427/390hp Corvette engines, and Pontiac used it on their '67 4-barrel engines.

There are several problems with this arrangement:
1. 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 nights in Southern California.
2. A carb bolted directly to a steel shield is highly prone to vacuum leaks between the carb and the shield.
3. Any leak in the gasket arrangement results in exhaust gas ingestion directly into the intake manifold, which leads to poor engine performance and the possibility of engine damage if the leak becomes severe.
4. Since the “hot slot” was only used for a few years, there is a high probability of “mechanics” installing the incorrect carb base gasket (late model style), resulting in exhaust gas ingestion into the manifold and external exhaust leaks due to the incorrectly-fitting late-model base gasket.

To solve this problem, you need to use a special 3-piece carb base gasket “kit” for the “hot slot” manifolds. There are no parts stores who recognize the existence of such a gasket kit, so you have to create your own (I am no longer offering these for sale).
Here is a typical cast iron Chevy “hot slot” “smiley face” manifold. The slot was also used on the aluminum Chevy Big Block manifolds, ’66-’68 327, and on 1967 Pontiacs. The “hot slot” is the long groove running from side to side just forward of the small primary throttle bores.







pont carburateur.jpg

Edited by cquisuila (see edit history)
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...