There’s the Problem!
Just at close of day today I realized that Carbot had the old 1.6MHZ 1802 board in it. I had noticed it was sluggish but I really twigged when I tried to figure out why it wasn’t hugging the wall. The olduino times the pulse by spinning in a tight loop counting loop passes. with the CPU running at < half speed it was reporting distances as much shorter so it was trying to get 2.5 ft away from the wall! It would also affect all the delays but i had been diddling them anyway so less effect there. Anyway, I’ll carefully restart tomorrow.