2g Carb Connection Help

Who knows what these two hoses go to? I assume they are vacuum but route to?
Thanks.

 

The one on the bottom goes to the vacuum advance on your distributor. I don't know what the upper connection is for though (the 2G carb on my '67 doesn't have that one).

 

upper one may of gone to the air cleaner

 

The upper one is not vacuum, it's s fresh air source for the automatic choke.

 

It’s a manual choke.

 

I see an automatic choke housing in your picture

 

It’s not. It has a lever and goes to dash with a pull.

 

It may have been converted but that was originally an auto choke carb. You can just plug off that upper port.

 

can you show a pic of the complete choke housing area?

 

I am seeing a later model 2g with a auto choke . might have been converted
top fitting is a smog connection
bottom is vacuum

 

If it's been converted to manual choke, then cap the air horn connection.

 

If the bottom is a vacuum then it appears they are two different size connections. What should I use as the PO option doesn’t sit well with me.

 

Yes the vacuum port should be the same size as the one on dist. vacuum canister.Have you ran the numbers on your carb to see what vehicle it is from. May pay to get correct carb for your jeep. Seems backwards to convert a auto choke to manual.

 

These auto to manual conversions are usually not done completely correct on the Rochesters. The auto choke uses a small vacuum passage into the intake manifold to operate the auto-choke and is usually unknown to the modifier.

 

I thought the smaller top port was for the Autochoke and the lower larger one is for the Distributor? That’s where it goes now and that is what I’m trying to figure out why two different sizes.

Should they be routed diffetently?

 

The port at the bottom of the carburetor should be "ported vacuum." It is different from "manifold vacuum" only at idle. There is a passage from the port to the venturi, and that port is physically blocked by the throttle plate when the throttle is closed. Ported vacuum goes to zero at idle. At any other speed, it's the same as manifold vacuum.

Ported vacuum is often used for distributor advance, so that idle has less advance than otherwise. You can alternatively use manifold vacuum for vacuum advance, with worse emissions. Ported vacuum is also used to control the EGR valve, which I presume you do not have.

The port at the top of the carburetor is up in the "air horn" and sees atmospheric pressure - no vacuum. It's there as a source of clean air (inside the filter housing) that is channeled to the automatic choke. The small orifice in the automatic choke body that Walt refers to connects somehow (depending on design) to manifold vacuum. This places a very slight vacuum on the hose from the air horn port so that clean air is drawn into the choke heater. This heater is typically in the intake manifold where the air is heated by the exhaust heat from the exhaust crossover in the intake manifold. This heated air continues to be drawn into the choke housing by this small vacuum, where it warms the choke element and eventually opens the automatic choke.

 

Since this engine is a transplant, we don't know what devices the ported vacuum powered and what plumbing was there. Usually the port tubes are pressed into the carb body, and cannot be changed. If you need to change tubing size, there are adapters available.
Dorman Products - 47308

You should check these plastic fittings every few years. IME they age and break after a while.

 

You can see the identified (choke vacuum passage) comes from the base mounting housing. It's hard to see but there is a dotted line showing passage to the base.

 

Thanks. Yes I can see how it used to be a auto chock and now there is a manual setup so there would be an extra port. I guess I’m still wondering if the larger port should be adapted (appropriately) to run a smaller tube that goes to vacuum advance on distributor?

I also see there are other vacuum lines on the back side of the carb that have been blocked off.

so one goes the the value cover, one to brake booster...