The Stovebolt Site Forums The Shop Area Engine Shop Rochester Carb Questions - Help

The good news is that we got the 61 apache running this weekend after 8 years sitting in a field. New plugs, plug wires, points, etc...and after boiling out and relining the gas tank, replacing the sending unit and all gas lines, and rebuiling the carb, she started and seems to run pretty well. My questions revolve around the carburetor which I believe is a Rochester model BC which has an auto choke. This is not the carb that came on this truck as the manual choke cable was unconnected and loose when we first got the truck, and there is no place to connect the cable on this carb.
My first question revolves around understanding how this auto choke functions. There is a tube that butts into the top of the manifold and goes into a round section on the side of the carb which has a cover that turns to adjust from lean to rich. In disassembly, the spring inside this unit was not connected to the tang inside--we have now put the cover on correctly. It looks like the tube picks up heat from the manifold which in turn relaxes the spring which opens the choke. How far it opens/closes is determined by the position of the cover. Is this correct or am I off base?
My second question then is that there is a cross piece shunted into the top of the carb which takes a threaded rod that holds the air filter assembly. When we got the truck, the rod was threaded all the way into the throat of the carb, forcing the butterfly valve open and thus not allowing the choke to work. The engine ran fine like this, however it was a warm day, and we had been dinking with the truck all afternoon. I can unthread the rod so that the butterfly valve is closed, which seems to make sense, but it was not in that position when I got the truck.
Sorry for the long post, but I'm confused and would very much appreciate your opinions/expertise on this before we proceed further.
Thanks!

Sounds like they didn't have the choke working properly, so the used the breather stud to hold it open all the time. The spring is heat activated, and the adjustment controls the temperature when the choke closes. The tube is supposed to be connected to a sheet metal housing on the exhaust manifold, but if you cut the end of the tube square and run it to where it butts into the manifold it will work. When the manifold is cold, the choke should be closed, as it warms the choke will open.

You are correct on the threaded rod part. The original rod had threads only a short way up so it couldn't be screwed down in to the choke plate. Try some thread sealer or add a lock nut to hold it in place. It sounds like you have the automatic choke figured out. Only thing I not sure about is the heating tubes. The one going to the baseplate should be the return line. Someone more qualified then me we be along shortly. Joe

I run a BC on my 261. There is a vacuum operated piston in the choke housing that the line to the base connects to. It serves to draw hot air into the choke housing and to serve as a choke pulloff.

If it was my truck I would make a trip to the junkyard and get all the parts to go back to the manual choke,it sounds like someone put a carb from a car on it. I cant stand auto chokes as I have had some I could not get to work like I wanted it to. If you are interested in the manual choke parts email me as a local junkyard has a few trucks with the 235s still in them and it would give me an excuse to go roaming in there again. Jeff

Most of the choke setups I've seen like that have a "stove" heated by the exhaust that the metal line hooks to. Just butted up to the manifold, I would think it would not open fast enough to comensate as the engine warmed up. You might be able to improvise by adding a bit more tubing and taking a wrap around the ex. man right where it comes off the port. Hopefully then you can rotate the thermostat housing so you have choke and fast idle when it's cold but it opens quick enough that it won't start loping as it warms up. Most parts houses used to carry kits that would convert that type choke to either manual or electric, but I don't know if you can get them any more.

Thanks to all of you for all the comments and information. It was very helpful. Now that we have rebuilt the carb and backed the rod out it seems to function properly. I will keep the manual choke cable as is because down the road I would like to go back to the original manual setup. I prefer having control over the choke manually. Thanks again!