Heat riser air tube adjustment

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Does anyone have info on adjusting the choke and heat riser air tube on a 37 Pontiac 6?  I understand there is a Bakelite adjustment to “lean or rich” for the choke.  When is it necessary to adjust that and what are the symptoms of adjusting it the “wrong” way?


  Also there is an adjustment on the air tube from the fan end.  That is part of the heat riser system.  What is the proper summer and winter adjustment for that tube?


i have poor running during initial warmup that I think is related to either the choke adjustment or the heat riser.  I also had one shut down that felt like running out of fuel or vapor lock and I think that is related to the air tube adjustment.  I can’t find any factory info on these adjustment and there are too many combinations to guess at them.

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I don't know, I can only tell you what I am doing (1936 Master Six).


There is a setting for the choke housing in the manual, and that is how I set it. (It would be something close to straight up, maybe a notch or two either direction). Yours would be close but possibly different. One would richen it up a notch if the factory setting wasn't enough, due to a tired thermostat or extremely cold climate or something, otherwise leave it alone.


Unlike some later cars with similar chokes, there is a piece of cork inside the choke housing, possibly used as an insulator, and a screen to strain the air drawn up the little flex pipe from the choke stove, because that air bypasses the air filter. You might want to look in there and make sure everything is in order.


The little butterfly valve at the end of the air tube, I can't remember how I have it set, but could look when I get home. Probably closed. The butterfly was missing, and I made one. I would set it for fastest heat riser opening, whatever that is. You want it to behave like a 1960's heat riser, heating everything up for a short period, then opening completely. I suspect the tube is to blow cold air, keeping the heat riser closed longer when the butterfly is open (it is radiator air, but the exhaust is probably hotter).


I imagine in 1936-37 the kerosene laced gas of the 20s was still fresh in everyone's mind, and they probably thought a bunch of extra carb heat would sometimes be necessary. Today, not so much.


Moving on down to the heat riser itself, there is one caveat. My heat riser weight is not original. It is a reproduction made by me from blurry whole engine pictures on the Internet. I think it behaves just like the original but don't really know. I believe the thermostat spring is correct and probably original but I can't prove that either. It works about like I would expect it to work.

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