I have the hot air with electric assist choke on my 77 351M. This motor is in my 74 F100. How do I check to see if it's heating up and working properly? I have power to it on run only. I took it off and held it in my hand with power to it. I held it for about a minute but couldn't feel any change in temp. How long should it take for it to heat up? Should I be able to feel it heat up by touching the spring with my bare finger?

Thanks
Mark C.

 

if it wasnt grounded to the engine , you wont get ahy heat , bob

 

Bob, How is it grounded to the motor? I only see the one plug for power on the cap. Does it ground through the carb somehow?This is my first Ford and my first attempt at trouble shooting this style choke. Any help is greatly needed.

Mark C

 

The electric-heated choke thermostat grounds through the carburetor body, via the shaft that the bimetallic spring engages.

The power source is the stator terminal on the back of the alternator. It should supply +6.25 to +7 VDC, only when the engine is running.

To test the internal ceramic heater element, you can test for continuity from the spade terminal to the center of the bimetallic spring. No continuity means the element or its connection is broken, and not working.

If the ambient air temp is over 40F, you can test the heater element's function by temporarily plugging off the air source for the choke's warm air system.

Disconnect the hose from the 45-degree elbow fitting on the bottom right rear of the air horn, and plug that hose so it cannot pull air through the heat exchanger in the manifold. Then start the engine and see if the choke opens up after a few minutes (5-15 minutes, depending on the ambient air temp).

If the ambient air temp is very cold (less than about 25-30F), the electric heater may not be able to open the choke very much. The electric heater is designed to supplement the heat from the warm air system, to open the choke quicker than the warm air system could alone. If your choke has both electric heat and warm air, it is designed to use both systems to warm up the thermostat and open the choke all the way.

 

thank you ,bubbaf250, respectfully,bob

 

Yeah Thanks Bubba. Your knowledge is irreplacable.

Mark C.

 

Bubba, I did some checking per your instructions. My truck has a 77 351M in a 74 F100 and the wiring on this truck is a nightmare. It's been through many hands. I have no continuity on the spring. The only wire I can find, has 10v on it in run. Is this too much voltage and will this much volts burn up a new electric heater?

Mark C.

 

I don't think 10V will burn up the heater (very quickly), but it will make it hotter than it should be, and perhaps cause the choke to open prematurely.

Look on the back of the alternator case for a threaded terminal labeled "STA," or something like that. You may need to make up your own wire to run from that terminal to the spade terminal on the choke thermostat.