I have a Z1000 on my workbench. I've used it to do a conventional reset (1 horn, 5 bells) and got the confirmation of the reset from the engine. That's my go to procedure for problems like this on PS2/3 engines.
Of course, you have to have a good battery! (as posted above)
I did use a Z4000 trying the 18 up and down with the throttle on a PS1. It still ended up to be a battery issue. Once swapped out, the engine ran as expected. On one problem engine, I used an external charger to get the battery full. Put it back in and the engine ran.
Our grandkids have a few old MTH engines that sit for very long periods going unused. Those could probably benefit from the supercap replacements.