your dropping voltage across the circuit.backprobe the wire from the choke back to where you get source voltage.it sounds like you got high resistance in the circuit. use an ohmeter to check circuit.all cars came with power to choke off of the alt.not all had full 12v to chokes.some used pulsed volts ie the voltage would be on and off while running. if you have a switched power source to the choke you feed voltage to it whenever key is on.so if you don't start the car but leave the key on you heat up the choke or if car stalls and key is on the choke will open anyway.result cold car warm chokes. that's why it's better to use alt.