automatic choke

I am trying to repair the automatic choke of my 1955 chrysler windsor - 301 poly V8. It works with a thermostatic coil spring heated by a hose from the exhaust manifold. I have replaced the hose that was completely obstructed, but the spring is still not receiving hot air.

I would like to avoid to remove the exhaust manifold, does anibody know how is made the heater element inside the manifold, and if is possible to clean it without removal?

The shop manual doesn't give any detail about the heater (the so called "stove"). I tried to blow air inside it, but it seems it is not possible. Is it obstructed or has it a closed end?

Thanks, Pierpaolo

This system probably works similar to what some of the early 1960s Chevrolet V-8s did, and like some of the 1977 Chevy V-8s did, but with a different configuration.

Basically, exhaust gas should not come through the pipe that goes to the choke, but what should go through that pipe is air that has been heated by the exhaust gas. On the inside of the integral choke housing, there should be a small hole that is connected internally to manifold vacuum. That vacuum draws the heated air through the pipe and into the choke coil mechanism. It's a calibrated vacuum bleed, of sorts.

Just like any other automatic choke, when the ambient air and metal temperature in the engine compartment is about 70 degrees F, the choke should just close when the coil tension adjustment is made by rotating the black choke housing on the carb housing it fits into. Not a hard close, but a soft one. This might result in the index mark being different than factory specs, but the bi-metal spring can increase in tension as it ages. This is a situation where using the factory spec is only a starting point and not an absolute adjustment point. It can require a little playing with to get the right choke action for your climate too, but too lean is usually a little better than too rich (and black smoke with fuel/oil dilution possibilities). Just loosen the hold-down screws and rotate the black housing as needed to get the adjustment that works best.

Also behind the choke coil in the carb housing can be a little piston and rod affair that is the "choke pulloff" to further crack the choke open once the engine starts. It works with a calibrated vacuum bleed pulling on the piston's backside to open the choke, just as the later external vacuum diaphrams did. I suspect this is the way your carb's setup, but it could also have the electric solenoid pulloff like the 1950 flathead 6 cylinders did.

Hope this helps,

NTX5467