I presume our American cousins are aware of this Ohio company but it was discovered over the weekend that yet another cause for the poor running of my 1977 GL1000 was air leaks in the Inlet Manifold Rubbers. Not surprising as they are almost forty years old now. I discovered that the rubbers (4) are vulcanised onto the alloy manifolds and that new replacements would be impossible to locate and old ones would most likely be just as hardened.
I found on the Net this company -
www.jbmindustries.com - who manufacture replacement rubber hoses for all sorts of vehicle using modern and more advanced rubber. The ordering advice page made amusing reading with the emphasis on the words 'ordering' - don't do this, don't do that or else, and so on.
Well the website does have a well illustrated page showing how to cut the aged rubbers off, cleaning of the alloy manifolds, and slipping the new rubbers on over the lip. They aren't cheap at around $130 incl. postage to the UK, but hey ho, I have no alternative.
I look forward to Ian Mason returning soon to tune the carbs yet again but with all the correct amount of air going into the carbs

BTW Ian is a true gent and has been down a few times now to see the bike, each time making small improvements. These new rubbers should finally make the last of the tuning straightforward.
"Time flies like an arrow, but fruit flies like a banana" (Groucho Marx).
"Outside of a dog, a man's best friend is a book. Inside of a dog, is very dark" (Groucho Marx).