Classic/Antique Car Repair: Rochester 4GC choke question, 56 chevy bel air, pivot shaft

Question
Paul:  I have a Rochester 4GC, #7026121, on my 56 Chevy Bel Air and have just tried to replace the automatic choke element, which I was told was bad (the choke would not close when the engine was cold, making it very difficult to start in the morning.)  I manually closed the choke when the engine was cold, then replaced the element with a new one, making sure that the hook on the spring faced the right way and was right up against the lever from the carb.  I put it all back together, but when I started the engine, it bucked and spouted smoke from the tailpipe, like there was no tomorrow.  The choke would not open, even after I kept the engine going and filling the neighborhood with smoke.  Numerous efforts to find the problem have been unsuccessful, so I'v manually opened the choke again and set the element spring 90 degrees out of the way until I can find out what's wrong.  Can you guide me through this and give me some advice on what I'm doing wrong?  thanks a bunch.......Bob

Answer
My experience with these is somewhat limited--my '55 Nomad had one and once it was properly rebuilt it ran fine.

Is the element cover adjustable by rotating it? If so, I'd back it off until the choke was just closed at ambient temp. Make sure your heat riser tube is open and its connection to the exhaust manifold is solid--it's transmitting heat and has to do so quickly for maximum economy and best state of tune.

Last, be sure the choke butterfly pivot shaft runs smoothly--if it's cranky or stiff, it will never work properly once the motor is hot.

--Paul