A few years ago I was lucky enough to buy a 1976 CB400f, one owner from new and just 4,000m, which had been in storage since 1978 and was completely original and untouched. As a bonus, the old chap, who I knew about 30 years previously had thoroughly drained both the tank and the carbs.....happy days.
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I recall having a conversation with Ash about the finish on the fasteners and plated hardware...... what I found is, many fasteners that appear to be plain silver bright zinc reveal yellow passivated threads when removed..that being their original finish.
I'm happy to be corrected but my understanding of yellow passivate is, the item in question gets zinc plated and as soon as it is removed from the plating bath it is further dipped into the orange passivating solution, giving that lovely pale yellow finish. But that finish is micro thin, hence, as it wears away with time and use, the silver BZP below becomes aparrent and it's hard unless you are the king of anoraks to remember what was there.
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Here are a couple of photos of my carbs as they came off the bike and after half an inch of fluff and compacted dust had been removed. look closely at some of the screws and fittings and you will see traces of yellow passivate. I recall concluding that pretty much everything on those carbs had received a passivate coating and that is how I restored them, although I don't have any decent photos of the finished carbs.
I'm always happy to be corrected, but that was my take on this subject........Mick.