Late C fitted with monoblocs at factory?

[Magnetoman]

So if you are fitting Monoblocs to a standard C with front and rear heads, do you use 389s (and not the 689) with the special rear manifold?

All I can say is that is what the Amal list specifies. For 1954 and earlier the Amal list shows the two different carburetors that were used on the front and rear cylinders, so it doesn't seem likely they forgot there was an asymmetry when they introduced the Monobloc. So, to paraphrase O.J. Simpson's lawyer, if the 389 fits, you must affix.

 

[hadronuk]

I have all the components mentioned, including ET32/20, and I can say for certain you will not be able to fit a 389 to the rear cylinder of a C without moving the battery, unless your ET32/20 or your bike is very different from mine.

 

[Spqreddie]

This is the current Amal list,
http://amalcarb.co.uk/catalogsearch/result/?q=vincent
and indeed their offer is in line with what mentioned by Magnetoman,
When it comes to Black Sahdow and Black prince model year 1955 they offer only the model 389/10.
http://amalcarb.co.uk/carburettor-for-vincent-black-shadow-black-prince.html
and as full set (two carburettor) they offer two of the same kind:
http://amalcarb.co.uk/ack338.html

And for sure they didnt forgot the rear one because if you look at a previous year in their Catalogue they make the difference between front and rear and even suggest the model to buy to make the set of two (quote: 289M/1DO Description: Carburettor for a Vincent Black Shadow (Paired with 289N/2DS)
http://amalcarb.co.uk/carburettor-for-a-vincent-black-shadow-paired-with-289n-2ds.html

So i think, here we have two hypotesys that i can not confirm,
1) they only made one side as with two front heads the black prince didnt need a different rear carburettor
2) given was early in the production run of the monobloc may be at the time it was only available with the float chamber on only one side

But so, today, given that at Amal they know the correct set up and jetting for the 389/10, if now one would like to have a monobloc set up on his bike could order to Amal a 689 to be made to "/10" specifications as per the 389 they have in stock for the black shadow/black prince in order to have the float chamber and primer on the right side for each cylinder.
But I do know if they do sepecial build, otherwise one could buy one of their specific 389 for black shadow/black prince and any 689 of the same bore, then when received, open the 389, check the jetting and do the same thing on the 689 and then start the carburation from there.

Thanks,
Edmondo

 

[Magnetoman]

I have all the components mentioned, including ET32/20, and I can say for certain you will not be able to fit a 389 to the rear cylinder of a C without moving the battery, unless your ET32/20 or your bike is very different from mine.

From Know Thy Beast:

Conversion of Series C to Monoblocs
...The easiest solution is to use a special double-flanged adapter ET32/20 which makes it possible for a Monobloc instrument to be fitted to the Series B or C rear head without modification to the battery carrier.

 

[hadronuk]

As I said in post 4:

Stevens page 188 mentions that monoblocs can be fitted to a C series using adapter ET32/20 "without modification to the battery carrier". I think he neglected to mention that this is only possible if the rear monobloc is an opposite handed 689 model.

 

[Magnetoman]

As I said in post 4:

Right you are. In my defense, that was ~6 weeks ago. But, I clearly forgot.

You mentioned a 689/003 in post #4, so I tried to find it (n.b. are you sure that isn't the mixing chamber number, not the type number stamped on the flange?). I have three Amal lists covering the time period in question. The pre-Monobloc 1940-1954 list shows the two different Standard carburetors for the Rapide and Black Shadow. Both the 1955 list, and the 1955-1961 lists show only the 389/10 for the Black Shadow and Black Prince. Scanning the lengthy list twice turned up no 689 carburetors at all. So, either I didn't scan carefully enough, or the 689 was introduced sometime after 1961. I suspect the latter. In any case, it seems pretty clear from the Amal lists that 389s were used on 1955 Black Shadows, so suspicion falls on the factory for having introduced an undocumented adapter flange (or, at least, an adapter that isn't known to any of us posting to this thread, although it may be well known to a few other people).

 

[hadronuk]

Right you are. In my defense, that was ~6 weeks ago. But, I clearly forgot.

You mentioned a 689/003 in post #4, so I tried to find it (n.b. are you sure that isn't the mixing chamber number, not the type number stamped on the flange?). I have three Amal lists covering the time period in question. The pre-Monobloc 1940-1954 list shows the two different Standard carburetors for the Rapide and Black Shadow. Both the 1955 list, and the 1955-1961 lists show only the 389/10 for the Black Shadow and Black Prince. Scanning the lengthy list twice turned up no 689 carburetors at all. So, either I didn't scan carefully enough, or the 689 was introduced sometime after 1961. I suspect the latter. In any case, it seems pretty clear from the Amal lists that 389s were used on 1955 Black Shadows, so suspicion falls on the factory for having introduced an undocumented adapter flange (or, at least, an adapter that isn't known to any of us posting to this thread, although it may be well known to a few other people).

Morning Magnetoman.
I think perhaps the numbering of carburettors supplied by Amal as aftermarket upgrades were not recorded for posterity. The current Amal Company seems to have incomplete records of the companies’ earlier history.

As well as my 689 having been sold as "from a Black Shadow", there is a local Rapide that was sold to it's current owner with 389 front + 689 rear fitted, apparently as a period fitting. Presumably, whenever 689s became available, they became the preferred choice for the rear.
My copy of "Know thy Beast" has 1972 as the earliest publication date, so 389 + 689 could have been well established as the standard offering from Amal by then, so E. M. G. Stevens may have simply presumed that a 689 would be used.

I see in MPH 85 (1956?) there is an article about making a special adaptor for fitting a monobloc to the rear of a C series, and it states "the battery will need to be moved about 1.5 inches". Which would seem to prove ET32/20 and 689s were not available at that time.

Incidentally, Amal kindly supplied me with scans of the original build sheets (earliest dated 14-6-1946) for the 276 pre-monoblocs as specified by "Mr Irving", with many hand written notes including "throttle slides selective fit". What did you get if you did not specify this ?!!
I will post here or send you copies if interested.

 

[Magnetoman]

Presumably, whenever 689s became available, they became the preferred choice for the rear...
I see in MPH 85 (1956?) there is an article about making a special adaptor for fitting a monobloc to the rear of a C series, and it states "the battery will need to be moved about 1.5 inches". Which would seem to prove ET32/20 and 689s were not available at that time.

Very interesting. However, since 389s were supplied on both cylinders by the factory, it still leaves open the question of whether those few bikes supplied that way in 1955 had modified battery trays, or had some undocumented variation of the ET32/20. Someone must know the answer to this.

 

[Spqreddie]

By looking again at Amal website, it seems that they do not produce 689 as of now,
in their on line catalogue only 389 are only mentioned,
so if ones would like to try the conversion needs to find an used one.
Eddie