I've got a pretty good idea what needs to be done to make the Pot Box throttle keep the transmission happy, while making it rev higher, longer (to suit the electric motor). It's all been flowing around in my head and it's finally come out on paper.
Firstly, there's a photo of the throttle in a previous post. It pivots when the accelerator cable (top) is pulled (by pressing down on the pedal) and this pulls the transmission cable (bottom) out to tell the transmission "I'm revving hard, keep it as low as you can for as long as you can".
I want to keep this information flowing, even increase it (to suit the higher - revving electric motor) while using the electric motor and pot box instead of the petrol engine.
So: I need to find out some specs. Here are two diagrams of the throttle assembly, showing it at "closed" and "open". As you can see from the red arrow, the top bit is pulled to the right by the accelerator pedal cable.
In the second pic, I need to find out the distance described by the red arrow. This will tell me the information I need to "maintain" when replacing the throttle. If "pull transmission cable out 3cm" = "Keep it in for an extra 1,000 RPM" that's the distance I need to replicate when linking the accelerator pedal cable to the Pot Box. Since the Pot Box has a shorter arm (and therefore travel distance), I'll need to modify/extend a lower arm to keep the transmission happy.
I'll be seeing my wife's grandfather (retired engineer) at a party tomorrow night, and I'll put it to him as an engineering challenge. I'm sure he won't be able to resist.