I have a 1985 Ford E-150 Van (V8 302) with a Motorcraft 2150A 2V feedback carburetor (part number E5TE-9510-YA) and EEC-IV electronic engine control (computer).
When starting cold, the choke pulldown function fails. The choke closes completely and fails to maintain the minimum choke pulldown setting (choke opening of 0.15 inches) once the engine is started. If I can keep the flooded engine running until it warms up, the choke plate eventually opens up and the engine runs OK. To me, this implies that the thermostatic components of the choke are working fine.
I first tried to adjust the choke pulldown with the vacuum diaphragm adjustment screw in the choke pulldown unit. I then removed the choke pulldown unit to check to see if the diaphragm had failed. It was fine. Only then did I discover that there was no vacuum on the line leading from the carburetor (base of carburetor) to the choke pulldown unit.
I removed the short hose and checked for vacuum (finger suction) at the long metal nipple protruding from the base of the carburetor. There was none. I then ran a longer hose to this nipple and tried to blow /suck air through the passageway with the engine off. It was completely blocked. I squirted carb cleaner down this nipple, let it work, and repeated my attempts to blow / suck air through the passageway. It remained closed. (There did not appear to be any vacuum leaks around the base of the carburetor.)
Rather than using the vacuum from this blocked carburetor port, I decided to derive the choke pulldown vacuum off another vacuum line originating at the intake manifold. I think this is OK because I think the choke pulldown vacuum originates in the manifold anyway and is routed up through the carburetor. (The original carburetor port was near the base of the carburetor assembly; I don't think the choke pulldown vacuum can be derived from the carburetor venturi because I think the choke pulldown vacuum must be present before the throttle is opened and the carburetor venturi vacuum is created.)
Question Set #1: Is the choke pulldown vacuum supposed to originate in the intake manifold, as opposed to carburetor venturi? If so, why would this vacuum line come out of the carburetor, rather than from the intake manifold vacuum tree (as I've now rerouted it)?
Question Set #2: I think it is rare that a carburetor vacuum line would be completely blocked by dirt. Since this is a special feedback carburetor, is there a carburetor solenoid failure or feedback sensor failure that would cause this normal choke pulldown vacuum circuit to switch into a closed position?
Question Set #3: Assuming that the previously discussed carburetor vacuum port is blocked because of a problem / failure, are there any other performance consequences due to this blockage? So far, the only obvious problems were related to the choke (black exhaust smoke and fuel flooding until engine warms up). The engine always seemed to run OK once the engine thermostat opened. Now with the choke pulldown vacuum reestablished from another source, the choke seems to work fine also.
Question Set #4: Since I reinstalled the choke pulldown unit, I have noticed the idle speed has increased, even after the engine has warmed up. However, I think I mistakenly readjusted the fast idle cam setting while reinstalling the choke pulldown unit. If I am not mistaken, the choke pulldown unit (and the associated vacuum) plays no part in idle speed once the engine warms up and the thermostatic choke takes over. Is this your understanding?
Knowledgeable answers to any of these questions would be very helpful. Thank you for your assistance.
By the way, these feedback carburetors were used in mid-1980 US Ford V8 vans (E series: E-150, E250, E-350), trucks (F series: F-150, F-250, F-350), and some Broncos.