Adding to Warren's information: The '73 CIS cold start circuit only works while the starter is cranking and if the hand throttle is pulled up enough to engage the micro-switch on the side of the throttle housing. After the engine starts and the starter is no longer running the WUR is what controls the system during warm up. However, the hand throttle if it is pulled, helps by holding the throttle open and causing a higher idle. Check to see that your hand throttle is causing the throttle linkage to move and engage the microswitch on the side of the throttle body (driver's side). If not, the attachment fitting from the hand throttle to the throttle linkage rod in the tunnel between the seats may have loosened or broken. I think you may be able to access it by reaching forward through the hole that grants access to the shifter coupling (under cover behind the seats).
Jim