Resurrection - as said, solved the problem by borrowing a petrol screw Dellorto from another bike and ran it till about a month ago. Decided it was time to replace carb and return the original to the donor bike when the new one turned up. I expected to notice a real difference between a brand new carb, and a 25 year old one. Virtually none, which was a pleasant surprise, and goes to show that they are/were very good quality. (this is contrary to the opinion voiced on a well known site, which claimed they wear significantly in a year)
