I have a carter afb that has an unusual choke setup. It has the bi metal spring that opens the choke when heated, but it has no provision for a heat riser and its not electric. It does have a vacuum tap. I thought maybe they ran the vacuum supply thru a ported vacuum switch and used that to pull the piston down to operate the choke, but thought better of that when I discovered that the tap is a vacuum source. So what is the heat source for this choke? The number is C3 9637 S. I believe that's from a early 60's ford. Trying to figure out how to make this choke work properly with the 302 I want to put is on. I could switch to a electric conversion, just trying to save a bit if possible.