1974 Spider Hand Throttle Question

[Britalia]

How is this supposed to work on a Spica car. I can get mine to hold a throttle position if I step on the accelerator first and then pull on the hand throttle knob. What are the main parts in the engine compartment that the cable attaches to. My cable just has a round barrel on the end of the cable. The cable passes through a large hole in the throttle bell crank. When the cable is pulled the round barrel pulls up on the bell crank.
There is a large spring below the bell crank, but it was so stiff that I removed it in order for the hand throttle to work at all. Throttle actuation seems fine without the spring. I suspect a weaker spring was original.
A picture or diagram would be appreciated and helpful. I think my car is missing some parts.
Thanks for the help.
Chuck

[Farace]

I also press the accelerator while pulling the knob. Then give the knob a twist and it will hold its position.

Do not use it as a cruise control. Frankly, while I find it useful because I've yet to get my car to have a fast cold idle, I'm not sure what its intended purpose is, since with the Spica adjusted correctly it wouldn't be necessary to use it for warm-up, and I've not found another use for it.

[Anfanuts]

See link here for this topic. (LINK)