Author Topic: Original BZP finish on CB400F carbs?  (Read 244 times)

Offline AshimotoK0

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Original BZP finish on CB400F carbs?
« on: January 30, 2020, 01:13:32 PM »
Not sure about the original BZP finish on CB400F carbs when new ... chrome passivated or not. Anyone know? Or could it be either?

Confused because NOS carbs below has yellow chromate passivate but NOS spare parts don't. :-\



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« Last Edit: January 30, 2020, 01:15:06 PM by AshimotoK0 »
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Offline Laverda Dave

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Re: Original BZP finish on CB400F carbs?
« Reply #1 on: January 30, 2020, 01:50:56 PM »
Ash, When I rebuilt my first 400/4 back in the mid 80's the carbs were definitely BZP silver finish. I remember the choke lever being rusty on the front face but the rear was still silver finish.
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1977 Rickman Honda CR750
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Offline AshimotoK0

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Re: Original BZP finish on CB400F carbs?
« Reply #2 on: January 30, 2020, 03:38:30 PM »
Ash, When I rebuilt my first 400/4 back in the mid 80's the carbs were definitely BZP silver finish. I remember the choke lever being rusty on the front face but the rear was still silver finish.

My first late 1976 one was just over a year old when I bought it and I don't remember carbs being gold passivate  either Dave .
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Offline mattsz

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Re: Original BZP finish on CB400F carbs?
« Reply #3 on: January 31, 2020, 12:10:16 PM »
Sorry for the little hijack here...

Not sure about the original BZP finish on CB400F carbs when new ... chrome passivated or not. Anyone know? Or could it be either?

Confused because NOS carbs below has yellow chromate passivate but NOS spare parts don't. :-\

So is "yellow chromate passivate" and "gold chromate" (mentioned in your "Witch's Brew" thread) the same finish?  I'd wondered aloud about that finish in my project thread - the engine-side "clutch lever" was rusted where water had infiltrated through the cable opening, so I soaked the rusty bit in distilled white vinegar.  The acidic vinegar zapped the rust, but also the yellowish finish of the clean metal:



It's hidden away, so I'm not bothered by the two-tone color...

Offline kettle738

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Re: Original BZP finish on CB400F carbs?
« Reply #4 on: January 31, 2020, 12:48:28 PM »
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.

Offline Nurse Julie

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Re: Original BZP finish on CB400F carbs?
« Reply #5 on: January 31, 2020, 01:20:28 PM »
We have certain  carb parts yellow passivated and you are correct Mick. They are BZP'd first and then dunked in the passivate and it is a very, very thin layer of passivated that is attached. It also wears off very easily and quickly.
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