Andy wrote:The MC21 T.P.S. part number is 04101-KV3-770.

While they have been known to fail, it is extremely uncommon in my experience. The T.P.S. is actually rather expensive new to replace, but I would be very surprised if you sourced some used carbs and they too had a faulty sensor.

Personally, I've come across it probably twice in 15 years.

Andy -- I did the tests suggested by Charles - and posted my results, however - haven't heard from Charles? Can you please take a look at my post (a few back from here) and see if my test results made any sensible conclusions. From what Charles advised - and what I found -- it appears the TPS is at fault?
Thanks for the help,
Brid.