Forget the crummy, nonadjustable, cold-blooded factory choke setup. Get a № 1232 electric choke kit. The choke lever on the 318 carb is different to the one on a 225 carb, so you will have to make a new choke pushrod and/or make a lever adapter as shown here (spaced outward from the carb toward the valve cover as needed), unless your 318 carb is a late-enough model to have the choke lever attached with a screw into the end of the choke shaft rather than swaged on and you can find a 6-cylinder choke lever to swap on. In that case, you can just use the 1232 choke kit as delivered.