Eric, re. Motorcraft 2100. In an old thread you described an exhaust manifold choke heat fix. If I understand correctly the two tubes coming out of the exhaust manifold do not open into the inside of the exhaust manifold but open only into a cavity in the cast iron which, of course, contains hot air heated by the exhaust. One of the tubes (which one???) conects to vacuum ??? and the other connects to the threaded fitting on the carb opening into the choke (heat) chamber. If one tube is connected to vacuum I can't figure out how heated air is drawn into the choke thermo spring chamber. Is it possible that one of those tubes is connected to the clean choke air tube (not vacuum) which is on the floor of the air horn plate and vacuum, which draws the heated air from the passage in one of the "legs" supporting the choke apparatus, is the vacuum source? I think I've figured it out.

I still don't understand your fabrication of a secure way to attach those two tubes to the exhaust manifold. I understand everything except the "bend the tube around a round object like a broom handle or use a tubing bender". Don't those two tubes just exit straight out of the holes in the exhaust manifold? Why the coil bend? Why not just get rid of those tubes, plug the holes in the manifold, or not, since they don't open into the manifold and run an electric choke and the heater hose running right next to the plastic choke spring housing to operate the automatic choke...Better yet why not just install a manual choke? Your expertise is much valued!

 

As far as the vacuum goes, there is usually a vacuum line fitting on the rear of the top plate behind the choke assembly. It just draws in a little bit of air as air is pulled into the carb. It doesn't connect to direct manifold vaccum.

 

I am 99% certain that, with the help of a much earlier thread, I finally have the vacuum and carb choke heat issues correct for a stock '76 F250 4X4 360 NP 435 just converted to a C6. Carb is a Motorcraft 2100. All of the rest of you guys probably knew this already but I'm a slow learner, I guess. I also started with someone else's idea of vacuum tube routing. First the obvious. One vacuum tube from the distributor advance diaphram to the carb right side port (spark port). One vacuum tube from the port on the front of the carb (EGR port) to the bottom port on the thermo reactive valve screwed into the intake manifold which opens when the engine warms up. One vacuum tube from the top port on the thermo reactive valve to the EGR valve. That tube has a one-way valve in it on my truck. One large tube connecting the PCV valve in the rear top of the right valve cover to the large port on the back of the carb near the mounting flange. Now the not so obvious. At least it was not obvious to me. The port at the rear of the carb in the floor of the air horn flange is connected to the largest of the two metal tubes coming out of the rear of the right exhaust manifold. The smaller of the two metal tubes coming out of the exhaust manifold connects to the threaded fitting on the choke heat chamber where the choke heat activated spring is. The two metal tubes don't actually enter into the exhaust manifold interior but only into a chamber connecting the two. There is vacuum in the choke chamber coming through a passage in one of the mounting legs of the choke apparatus which draws air from the carb air horn floor (that's evidently why that port is called the clean choke air port, because it's cleaned by the air filter before going to the choke as heated air) through the large tube into the chamber in the exhaust manifold, out the small metal tube, as heated air, and into the choke to heat the spring opening the choke as the engine warms up. The choke is also heated by the bracket which holds one of the heater hoses in contact with the plastic choke spring cap. If NE1 knows this to be incorrect or has any questions I'm all ears.