Hunted down some linkage shots of my '56 - the Demon carb has such a stiff internal return spring - I finally put a bolt and washer through the "over-travel slot". Still isn't sorted out. I think the whole thing will have to be redesigned sooner or later. Bird 55 has that Lokar set-up on his - I'd like to go that way too but haven't had time to sort out the details or do the work either one.
I put a positive stop on the back of the intake manifold so that the pedal always goes right back to a common stop every time. The main "return spring" on the linkage takes back to that pointand it seats. Use a stack of washers so it can't move - I could never get a stable adjustment without doing this.
When the pedal height is good (4-1/4" lets you go clear to full throttle when it hits the floor) and you are on the positve stop - then you use that Phillips screwdriver seen in the second picture to get the "kickdown" lever into the proper spot. The diagram arrow to "original pedal height adjustment" is a threaded "Z" bar that lets this be adjusted to fit. You want the foot pedal at the right height for neutral idle - and the lever for the kickdown to be at the proper spots.
Then you set-up the rod to the carb (after setting up the idle). The angular travel of the four barrel primary throttle differs on the OEM teapot - the Holley 4160 - and the Demon 525 - so I don't know how to predict what hole is best. I took a measurement of the distance from the butterfly shaft to the operating rod hole on the teapot - and tried to match it.
When you reach this point you want to remove the set-up screw driver and try out the throttle return system. Rev the engine with the foot feed and let it off abruptly. Everything should return to stable idle. On the diagram, points C-A-B are almost in a row - when I didn't have the stop screw in the slot and you slipped your foot off the throttle - the damn thing would jump clear up to a "reverse toggle" with "A" much too high and jam. Only the positive stop helped get this to work right.
When the thottle will go to full and return to idle with no hitches - then set-up the kickdown. You pull up (not too hard) snug on the operating rod until it reaches the stop in the transmission - then adjust the half clevis to "just" fit on the stub you see just above the blue band of the screwdriver in picture two. Add one thread for freeplay.
The "kickdown" on the Ford-o-matic is basically just adjusting a pressure regulator valve inside the tranny. This pressure is supposed to be an internal transmission indicator of throttle pressure/position. When the over travel slot isn't blocked (as I told you I did) - the foot pedal takes the engine to full throttle - and then the overtravel continues to raise the kickdown pressure still higher - unitl it decides to "kickdown" to a lower gear.
Steve Metzger Tucson, Arizona