Thanks to those of you that contributed. Very helpful and have added to my favourites. My local Honda Dealer is very helpful too, but it's nice to have the full breakdown of the various components when doing any maintenance. I had a problem with fuel starvation after running at high RPM for several minutes, and thought it might have been the full Pet **** in the tank valve assembly. Cause was a very slight kink in the vacuum tube from the inlet manifold to Fuel tank Valve. It wasn't obvious to look at as the tube itself has an outer plastic cover that is glued to the tube to keep it in place. In my case, the glue had gone hard and when the tube (and PVC cover) was pushed into its retainer on the side of #1 Carb, thetube became restricted by the small piece of hard glue pressing against it, and as a consequence, vacuum was reduced and reduced fuel flow from the tank resulted in the carbs running dry at full noise. took a bit of head scratching to sort that out, but a two hour ride yesterday without problems indicates a successful fixit job.