First, does the choke valve move? If yes, ok so far. If no, and the choke has an internal vacuum break piston, you need to clean the housing and get the piston free. Take the cover off the choke housing and you should see a lever and maybe a piston in a cylinder inside the housing. If the piston is stuck, soak it with carburetor cleaner to free it- that may not be easy to accomplish. If all that is working and the choke valve moves freely, ok. Put the cover back on and set the index mark on the cover to about the center of the Rich-Lean marks on the housing. Make sure the thermostatic spring engages the tab on the internal levers, otherwise nothing will work, no matter what you do.
Next, you need a heat pipe that connects to the fitting on the choke cover. The other end of the heat pipe fits into a cover on the exhaust manifold- called the choke stove. If everything is in order, when you start the engine, manifold vacuum through a port in the carburetor, pulls the vacuum break piston and opens the choke valve slightly. At the same time, manifold vacuum, through a port in the carburetor again, draws air through the manifold stove, through the heat pipe, into the choke housing, where the warm air heats the thermostatic spring to relax it, which then allows the choke valve to open slightly with air flow.
If the carburetor has an external vacuum break, it is a plastic chamber attached to the right hand side of the carburetor and connected (should be) to the choke mechanism. It should have a vacuum line attached to manifold vacuum. That device works like the internal vacuum breaks, but is a later device, and somewhat less troublesome than the internal breaks. But they need adjustment.
If you have any missing or stuck parts, you need to take care of that first. Then comes proper adjustment. Another matter.
Beyond the choke mechanism, there may be heat passages in the intake manifold that pass exhaust gas under the carburetor to help prevent carburetor icing during low-speed, cold engine operation. The heat passages need to be clear, or you will have poor engine operation during warm-up that no amount fussing with the choke will correct.
Keep in touch.
Harvester
