Re: Ford Feedback Carburetor Questions
Do you mean choke pull off???? If so, the choke pull off requires manifold
vacuum. This vacuum "break" action is require to allow sufficient air for
the motor to maintain rpm yet induce fuel enrichment through increased
signal to the venturis.
If the hose for the unit is assigned correctly and the available vacuum has
been checked with a gauge (sorry..the fickle finger just doesn't cut it) and
falls short, I would think that whatever is causing this is causing other
grief and the carb is due for an overhaul. Venturi vacuum is a very weak
signal and, in the 70s, was used along with a vacuum amplifier to control
EGR operation. Ported vacuum was used for distributor vacuum advance
operation but this signal is also too weak for choke pull off function.
"marv" <firstname.lastname@example.org> wrote in message
>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
> 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 closed 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
> 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.