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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.
 
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