Re: Choke adjustment on a 1964 Johnson 40hp
Ah yes, the 1964 automatic choke. Ok to answer the first question, put it on automatic and forget it. It regulates itself automatically. "Off" and "on" positons defeat the automatic function.
As for how it works, there are two systems working together. The first is a bi-metal coil that rotates the choke shaft in response to heat applied to the bi-metal coil. There is a special vacuum port in the intake manifold, that draws hot air through the bi-metal coil chamber. The air comes from a heat exchanger in the exhaust cover, through that steel tube that is attached to the choke. The hot air system is mostly a warm-up choke to keep it running as the motor warms up after starting.
The second system is an electric solenoid that slams the choke tightly shut for starting. You say there is no switch on the dashboard---well there is supposed to be one, in the same plate as the hot light.
Now for the 1964 odd-part. For 1964, the electric choke solenoid was activated EVERY time you start the motor---hot or cold, it choked when turning the key to start. The switch on the dashboard was an OVERRIDE switch, that you could use to prevent choking when starting a warm motor.
The override switch was sort of a goofy idea, but so was the idea of choking a warm motor. Very few people understood the system, and many had trouble starting their warm motors. Newer models replaced the override switch with a CHOKE switch, which works in the conventional manner. Press the switch to choke it when starting a cold motor.
Now for the rest of the story. Many of those override switches got replaced with choke switches, to make the thing work in conventional manner. I don't know which one you have. You will have to watch the choke to see when it operates---every time the key is turned to start, or only when the choke switch is pressed. Oh yeah, that's right--you say you don't have any switch at all. Well you are supposed to have one. Get a "choke" switch.
One last thought: Somebody may have replaced your key switch with a push-to-choke switch. Works just like the two separate switches, except the functions are combined in one unit. Turn the key on, push the key in to choke it, and hold it in while continuing to turn it to run the starter. I'll bet that is what you have.
