78 CJ7 Carb question

[Air Force]

What the heck are these two tubes on the passenger side of my carb? It is a 78 CJ7 , AMC 304 with a 2100-2 carb. I am in the middle of a frame off restoration. I was taking the engine apart and these two tubes were broken off at the manifold. I cannot find anything in the TSM, or on line about them. They are a hard line and run from the right side of the manifold to the right side of the carb. This is the one part of these jeeps I have no clue about (carb) I tend to stay away from them, but had no choice in the matter if I wanted to do this rebuild correct
http://www.jeep-cj.com/gallery/files/5/6/4/9/carb.jpg

 

[elwood blues]

Those tubes transfer heat from the intake manifold to the climatic (aka automatic) choke. As the intake manifold warms up to operating temperature, the heat is transfered up to the coil inside of the climatic choke, thus slowly closing your choke.

I have never tried to replace them, sorry I can't help you on that end

 

[Air Force]

Thanks. So they are not vacuum lines? Any idea what the disc part of the tube is about halfway up? Just curious that's all. I have tried to locate replacement ones, but cannot find them anywhere. If anyone has any leads I sure would appreciate it.

 

[priceg]

It would be quicker and cheaper to put a manual cable on it.

 

[elwood blues]

No, they are not vacuum lines. They are copper tubes, only there for heat transfer. The disc is nothing more than more surface area to transfer heat to. I originally looked for the correct tubing and everything when I swapped over to the MC2100 on my AMC 258 i6 / 4.2l , I never was able to find anything either.

 

[gert]

That is what the factories considered the most trouble free and releible methode to get the carburator to sense tempeture and operate the choke accordingly since not many people replace that stuff their probably isnt anything out there unless you fab it your self

 

[Air Force]

Thanks to everyone for the info. I am glad I asked. Always good to learn something new. Not sure what I will do about them, but I now have the knowledge to make an informed decision.

 

[csuengr]

They help OPEN the choke, not close it. Just make a plate to cover the hole on the intake and get a full electric choke housing. A full electric choke is easier than a manual choke. I have never had problems with mine. I just adjust it to summer or winter settings.

 

[elwood blues]

Here's what I did with mine. I simply cut off the copper tube, doubled it back on itself and made it so that it sits really close to the exhaust manifold. I have the AMC 258 i6 / 4.2l , sot that's a little easier, but I'm betting that the same thing would work just as well for you.

 

[elwood blues]

They help OPEN the choke, not close it.

An area of the carburetor generally misunderstood is the function of the automatic choke. Automatic chokes use a bimetallic coil to close the choke plate, and vacuum to open the choke plate. It is important to understand that the bimetallic coil does NOT open the choke. Automatic chokes are of two types: integral, and divorced (also called remote). The integral choke is an integral part of the carburetor. The divorced choke resides on the manifold (divorced or remote from the carburetor) and has an operating rod from the choke to the carburetor. In general, carburetors with divorced chokes use a separate choke-pulloff to open the choke. Integral chokes have a piston inside the choke housing. In general, the bimetallic coil rotates when cold to close the choke. As the bimetallic coil is heated, it relaxes, and the choke is pulled open by vacuum. In the case of the integral choke, there will be a tiny vacuum passage from the throttle area (vacuum source) up to the choke housing where vacuum is exerted on the piston. If this tiny passageway is clogged (often), no vacuum is applied to the piston, and the choke does not fully open.

Read the rest here: THE CARBURETOR SHOP / Troubleshooting

 

[IOPort51]

Manual chokes are a PITA and the last resort. If you can make the auto choke work it is will worth the effort. IMHO

 

[csuengr]

Mine both closes the choke and opens it. Model 2150-3. I have no vacuum source into the choke housing, or any kind of piston. There is a separate vacuum motor at the rear of the carb that handles the pull-off function, but only opens the choke enough for the engine to run. It has no effect on opening the choke. The bi-metalic coil actually does the opening, and closing.

 

[csuengr]

Forgot to mention that if you remove the tubes, the tube with the rubber vacuum hose that goes to the top of the carb needs to be plugged. There is a protrusion on the top of the carb that I put a dab of RTV in. Otherwise, the card will whistle and make other unwanted noises.