Rochester 2GC Carburetor Question

[Machine Gun]

I picked up another 2GV that I will put on my '64 Skylark to replace the troublesome one that I've been using. Interestingly, the replacement unit is missing the internal vent tube that vents the bowl into the air horn right  beneath the air cleaner. The tube on the old carburetor seems to be staked in so it's not a simple matter to move it to the new one.

 

My question is, how necessary is it to have a tube installed there? Whether or not there's tube installed the hole, the vapors will still vent into the air cleaner. Given that the manufacturer put a tube there I assume it's needed for something.

Edited December 20, 2023 by Machine Gun (see edit history)

[61polara]

The vent  tube is important.  You have a defective rebuild and I would return it because of this.  You may be able to remove the tube from your old carburetor and install it in the new one.  It's only a press fit.

[NTX5467]

As far as replacement, you can check the OD with a digital caliper (abt $2.00 at Harbor Frt) and then get a stick of fuel line at the auto supply in that same OD.  Cut and angle one end to 45 degrees.  Press in with some adhesive.  Done.

 

As the bowl is already vented via the bowl vent valve, which is closed ar a little bit above base idle speed, the necessity of that tube being there might be questionable as to really needing it.  Once the engine is running and air is going into the venturi, the float bowl should have a bit of positive pressure in it?  Might similar pressure be in it if the air just enters the venturi area, too? 

 

Your call . . . as to return the carburetor for another one, make a new tube, or use as-is.

 

I thought you had installed a Holley 2bbl that was working well?

 

NTX5467 

[Machine Gun]

The jury seems to be out on just how important the vent tube is. I decided not to send the carb back to get a tube installed for two reasons. First, I need to get the car up and running before the first snowfall and road salting so I can determine if the carb is working properly overall. I have a 90-day warranty. Sending it back now will almost ensure that it won't get back here in time before salt season starts. Second, I'm going to try running the car without the tube to see if I notice any deficiency in performance. If I do, it'll be a quick and simple matter to install a tube. It's 0.25" O.D. Hopefully sometime today...

[Machine Gun]

On 12/12/2023 at 10:21 PM, NTX5467 said:

I thought you had installed a Holley 2bbl that was working well?

I did, and I thought so. After a month or so I realized that it was working well enough. My enthusiasm for the new carb was clouded by the fact that it didn't vomit fuel upon starting after sitting for several days. I set a pretty low bar. I might have been quite satisfied with the Holley had I not become used to the 2GV, the particular flavor of which is tuned for a specific engine. 

 

The practically-new Holley is back in its original box and awaits my motivation to list it for sale.

Edited December 14, 2023 by Machine Gun (see edit history)

[JohnD1956]

Thinking about the problem, and not having had such an issue myself, may I ask if there is a spring that goes on the pivot bar for the float? If so I wonder if that is broken, or weak, or installed backwards, or maybe missing? 

[Machine Gun]

10 minutes ago, JohnD1956 said:

Thinking about the problem, and not having had such an issue myself, may I ask if there is a spring that goes on the pivot bar for the float? If so I wonder if that is broken, or weak, or installed backwards, or maybe missing? 

Good question John. If you're referring to the tang that connects the float arm to the needle, there is none. No spring anywhere else either. Some 2GVs and other carbs I've seen have one, but not mine. The service manual indicates that none is needed. I went for a totally different carb on the outside chance that there's something peculiar about mine that no one has been able to figure out. Wish me luck with this one. If the problem eventually returns I'll have a tough decision to make, whether I should set the car on fire or point it toward a cliff and put a brick on the accelerator.

Edited December 14, 2023 by Machine Gun (see edit history)

[Bloo]

What size is the tube? Could you just make one? It's probably some standard US size. Maybe brake tubing or modelmakers tubing? You sure don't want it falling out. I'd use loctite.

 

They started putting those diagonal tubes in carburetors in the late 30s. The bowl is vented inside the air cleaner so that the carburetor's fuel in the bowl is referenced to the same atmospheric pressure as the air entering the carburetor. Otherwise, dirt in the air filter, or even a different brand of air filter could cause a pressure difference that would change the mixture. I don't think they would bother to keep putting the diagonally cut extension on the bowl vent after all these years if it didn't matter. Maybe the air is less turbulent out in the middle where the tube ends? Not every design has a diagonally cut tube. The Autolite/Motorcraft 2 barrel for instance doesn't, but it has twin stacks in the casting sticking up about an inch. It still references the bowl to the atmospheric pressure inside the air filter. Presumably the tall vertical stacks accomplish the same thing the diagonally cut tube did in the 2GV. You can see the twin stacks (bowl vents) in front of the choke plate in this pic.

 

 

 

 

[Machine Gun]

@Bloo The tube is exactly 1/4", fortunately it's a standard size. I can easily make one.

[Machine Gun]

I installed the replacement carburetor yesterday and road tested the car. It performed well, just as I hoped it would. As for the vomiting of fuel, whether that problem has finally been taken care of remains to be seen over time. So as it now stands, my carburetor woes seem to have been "solved" for the Nth time.

 

I didn't install the vent tube. I have a length of 1/4" tubing whose OD measures exactly the same as the one in the old carb, yet the fit is so tight I'm afraid that I'll damage something trying to get it into the hole. Considering that the car runs just fine as-is I'm going to leave well enough alone for now. The real test will come when I drive in various traffic and weather conditions to see if I notice any issues. If I do, I'll deal with the tube then.

 

The car is now in hibernation. Thanx for your comments.

[Frank DuVal]

Plumber's sand cloth.😉 Unless you have lathe. Any sandpaper of 100 or higher grit. It will be ready to install by spring.

 

Warning, though, if it is too loose a fit, it will fall out, then we will be answering how to replace a piston questions, so tighter is better!😮

 

🦃🕎🍲☃️🍠🐖🎄🎄❄️

[rodneybeauchamp]

Jim, not sure if I mentioned it here but there are some great factory resources put out by Rochester on the rebuild and setting up of their series of carburettors. If you search Rochester 2GV guides ( may come up through Mikes Carburettor Service) you will find genuine manuals for rebuild and setup that are invaluable.

 

Once you can identify the tag numbers the rest is straight forward. I found them useful on my ‘63 Skylark with the 4GC and printed off the relevant pages. There are some great original resources out there but.

cheers

Rodney 😀😀😀😀😀😀😀

[Machine Gun]

3 hours ago, rodneybeauchamp said:

Jim, not sure if I mentioned it here but there are some great factory resources put out by Rochester on the rebuild and setting up of their series of carburettors.

Hi Rodney:

 

Thanx for the tip on available resources. I did download the Delco Rochester service manual some time ago. Unfortunately it didn't provide any clues as to why my carb acts the ways it does, which is why I opted to get a completely different unit. For whatever reason I decided to hold onto my core. I will clean it and store it away. It performed flawlessly apart from the overflow issue described on this forum ad nauseam. 

[XframeFX]

On 12/15/2023 at 5:12 AM, Machine Gun said:

OD measures exactly the same as the one in the old carb, yet the fit is so tight I'm afraid that I'll damage something trying to get it into the hole.

Like Throttle Shaft screws, don't want that tube to come loose and fall down past the throttle plates into the plenum and worse towards a cylinder!

Kinda difficult to drive that tube in-place especially with that angle at the top. Today, that tube would be plastic and glued in-place.

I'd leave it off.

[NTX5467]

I suspect the original tubes were freeze-fitted/(or perhaps a combination of heated casting and cold tube?) in production.  Throttle plate screws are always "staked" on their exposed threads to keep them tight.

 

Back in the later 1950s-carburetors, it seemed to be "stylish" to have the bowl vents sticking into the airflow as they did.  Rochesters seemed to be the most prevalent in this respect.  Kind of like they needed them on display in order to be a "good" carburetor?  By the later 1960s, those tubes had become "dull" and straight, by observation.  Kind of hiding in plain sight!  Which might well mean that them being there is more important than how they looked?

 

By this point in time, I suspect that most of the rebuilt carbs available are more "will fit" than "exact model fit", so might as well head up to a 1970-era 2bbl and adapt the linkage to fit your application, as needed.  Don't need a CA-spec carb, just a normal Federal-spec model.  That way, any evolutionary improvements in fuel metering which happened after the car was built would be in the newer-spec carb.  Would be important to compare the throttle plate size to the current model plus the holes in the intake manifold.

 

Knowing the size of the OEM throttle plates for that model year, then going up to about 1972 model year might find a 2bbl with those same sizes.  If the holes in the intake manifold are 1.75" or so, they you can go up to 1.69" throttle plates, which was common to many Chevy 350 2bbls back then, fwiw.  Although I tend to doubt it, the SAE Specs for 1970 claims the 1970 Buick 350 2bbl also has 1.69" throttle plates.

 

Happy New Year!

NTX5467