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
